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hydrofluoric acid

Posted by Albert Russ  
Albert Russ July 31, 2006 07:28AM
I was wondering if anyone could share some experience in cleaning and etching quartz with me. I have recently obtained some hydrofluoric acid and would like to use it to etch quartz in order to obtain interesting structure. I want the quartz to show clean however and I understand it needs to be completely submerged not to become frosted on surface. If more diluted acid is used I suspect sulfuric acid might speed up the reaction. The acid by itself is extremely slow with glass in relatively safer concentrations. Anyone with long experience in HF?
Jolyon & Katya Ralph July 31, 2006 10:19AM
The general policy on this board is not to give advice on the use of HF (other than strongly to give the advice 'DON'T USE IT') because of the extreme dangers of this substance.

There may be people who can help you with your issue privately, but this is not the place to give out information on the use of HF.

Daniel Russell July 31, 2006 12:41PM
There have been many allusions to the dangerous of hydrofluoric acid in the forums, but little detail.

You don't have to swallow hydrofluoric for it to cause injury or death. Because it is a lovely small molecule, it can be absorbed directly through the skin, and the vapours are absorbed directly through the lungs. When absorbed through the skin, it not only causes painful burns but also acts throughout the body to bind with calcium. This causes damage to the bones, but more importantly, makes calcium unavailable for critical chemical reactions in the body. One result can be heart failure.

A lethal dose of hydrofluoric acid can occur when as little as 2.5% (about the size of your hand) of the body's surface is exposed to concentrated hydrofluoric acid. You would be suprised at how little an amount of hydrofluoric acid is necessary to achieve that exposure. A geological lab technician in Australia splashed some hydrofluoric acid on his upper legs, providing exposure to an estimated 9% of his body. They amputated one leg after 7 days, and after 15 days he was dead of "multi-organ failure".

We all suffer from the (sometimes subconscious) "it can't happen to me" syndrome. But it *can* happen and it *has* happened.
Alan Plante July 31, 2006 03:08PM
Hi Albert

I hope that Daniel's post has made you understand why HF is considered to be a "lab-only" chemical, not to be used outside of a properly equipped lab, and most certainly not by people who are not trained in it's use.

You know, you can sit on a rock and toss a pint bottle of nitroglycerine back and forth between your hands day after day and not get killed by it - might even think the stuff is safe to handle. But just drop the bottle once...

HF is MUCH more dangerous than nitro - because you don't know that it is killing you while it is.

Anyway, if you are going to continue to try to use the stuff, please let us know where to send the flowers and charitable donations in your memory.


Phil B. July 31, 2006 03:44PM
That last sentence was original, Alan .

Albert: don't use sulfuric acid either! The only acids I use are hydrochloric 10% with special acid gloves and 5% acetic acid (white vinegar). Dont mess with quartz...

remember to DISPOSE OF THE ACID PROPERLY!!!!!!!!

Dr. Peter Haas July 31, 2006 03:45PM

10% sulphuric acid is considerably less dangerous than 10% HCl !!
Phil B. July 31, 2006 04:08PM
Nice! I might start using some. No one sells that here :( though there is some in toilet bowl cleaners.... but i dont want my specimens to smell like lemon.
Jolyon & Katya Ralph July 31, 2006 04:14PM
You can get sulphuric acid from car batteries.

But not much benefit in using it to be honest, I bought some small bottles of Conc. sulphuric a few years ago and the only thing I've ever used it for is cleaning the toilet! Hydrochloric is far more useful.

Zbynek Burival July 31, 2006 04:41PM
Sulphuric acid is not very usefull for cleaning. It forms many insoluble precipitates. Sulphuric is for me much safer then hydrochloric cause it has no agressive fumes but better do not spill it on yourself;)

All chemicals are potentialy very dangerous if handled improperly. Its only about knowledge and safety, theres no secret about HF - just must be used properly by trained person and in equiped lab. Nothing to be done at home!

The truth is that all mineral acids can cause serious burns or injuries when handled improperly. One must know his knowledge and equipment limits:)
Albert Russ August 01, 2006 07:36AM
Thank you guys for your replies. I should have told you in my first message that I have a very detailed knowledge about HF as well as all hazards associated with it. I am an analytical chemist (I ackgnowledge that I have experience with virtuallay everything including anhydrous HNO3, except HF) and I plan to use it in a well equipped laboratory where I work, full equipment using a digestor with negative pressure-I am not insane to do the work using liter volumes in my basement. Actually there is not much use in sulfuric acid itself except that it draws away some water and creates more oxidizing enviroment, if HF is diluted, addition of sulfuric acid speeds up the reaction. It acts than as more concentrated, if you mix sulfuric and nitric acid you also get the same results as if the nitric acid was far more concentrated by itself. I guess there are very few people that have direct experience with HF because it is not a usual nor practical chemical in a chemical laboratory unless it specializes in specific experiments that require it.
Albert Russ August 01, 2006 09:33AM
I read all your comments throughly and decided to share some knowledge with you on some of the most common acids. I hope it will be usefull. I try to write it as simple as possible.

HCl- is a strong acid, it is almost completely dissociated as well as H2SO4. It is perfect for dissolving carbonates and thus cleaning their surface, and many other minerals. It could be the most general acid in mineral cleaning.
Safety: As far as splashing, HCl is not as hazardous as other acids because its only power is its full disociation, H+ ions always have a place to bond on live tissue. I do not reccomend on trzing it, even if rinsed immidiately, concentrated HCl may irritate skin and destroy its uppermost level. However, there should be no further damage to tissue if rinsing is not delayed. Unlike sulfuric acid, it liberates HCl gas that is both irritating and toxic. The release of HCl gas is proportional to the acid's concentration. If mixed with some strong oxidiying agents, there is danger of chlorine gas liberation.
HCl itself does not possess oxidizing properties and is sometimes mixed with hydrogen peroxide to achieve this.

H2SO4- again a strong acid just like HCl. It can be used with similar results but its major dissadvantage is that there are fare more insoluble sulfates than chlorides. Its properties are very much dependent on its concentration. Diluted H2SO4 is only a strong acid, just like HCl. As it becomes very concentrated to anhydrous (100%), it becomes a good oxidizing agent and extremely hydroscopic. It is in fact so hydroscopic that it destroys tissue as it draws water from it and reacts with many organic compounds so that these compounds release even more water. As a result, plant and animal tissue can become almost carbon like. The advantage of this is that for instance an inert mineral can be cleaned from excess fungus and organic material with concentrated sulfuric acid- actually the acid does not remove this stuff completely but due to the destruction it makes it is much easier to rinse and scrub off afterwards. A disadvantage of this property is that concentrated H2SO4 is very hazardous because it pulls water from tissue, even from organic molecules and oxidises and releases H+ at the same time. Therefore spills of concentrated H2SO4 on body are much more dangerous than HCl or diluted H2SO4. Sometimes tissue destruction is immidiate and severe.

HNO3- is an acid in low concentration similar to HCl but produces very few insoluble compounds. It has significant oxidising properties which become very apparent at high concentrations. At higher concentrations above azeotrope (over 65%) HNO3 not only becomes highly oxidizing but at over 80% is hydroscopic and reacts with water quite intensely. It is not as hydroscopic as sulfuric acid though. Like HCl, it liberates toxic gases (NO2 mostly) which is not only highly irritating but also poisonous. At concentrations around 80% and over, the acid is fuming vigorously and is very dangerous to deal with. 65% HNO3 small contacts or splashes cause yellow stains on skin that peel off within days if washed immidiately. Fuming 80% acid or more causes severe burns on skin immidiately that are very different from the commercial concentrated 65% and differences are apparent even if washed immidiately. I had one bad experience in such. HNO3 is also very dangerous with many organic compounds at such concentration as vigorous niotration, oxidation or ignition can occur. HNO3 at such concentrations is not practical for mineral cleaning due to its dangers while better results can be obtained when carefully heating deluted acid.

HF- hydrofluoric acid is not a strong acid (it is much less dissociated as an aqueous solution because the hydrogen bond is too strong for free ions to form readily). Acid strength is defined in its dissociation in water, not in its other potentially hazardous chemical or physical properties. In fact, if HF was a strong acid, it would not penetrate tissue so well because H+ would attack tissue right from the skin sufrace, slowing the molecule's propagation. Obviously the undissociated molecule is very small which only benefits its fast penetration through tissue. Eventually it reacts with almost anything within the tissue, creating severe burns and tissue necrosis. At the same time, F- ion precipitates Ca2+ and forms insoluble CaF2. Drop of Ca2+ and Mg2+ in blood levels, called hypocalcemia and hypomagnesia in severe cases proves fatal because of their importances in many physiological processes including heart muscle functioning. Hydrofluoric acid is the only known chemical that effectively dissolves quartz, glass and other silicates. It is unfortunate because the only chemical possible is so dangerous. Glass can be attacked by hot concentrated phosphoric acid or molten NaOH or KOH, but the rate of attack is very slow and the results are very bad. I am not sure about quartz. HF, when concentrated enough, does not attack many metals and can be transported in steel tanks.

HOOC-COOH oxalic acid is best in removal of rust stains and selenite. It is a weak organic acid that bonds meny metals in very stable complexes.
CaSO4 for example is almost insoluble. Sulfates in general are extremely stable because sulfuric acid is a very strong acid which binds very well, and no acid is able to release sulfate ion into sulfuric acid and take its place. Usually weak acids that create salts can be released with a stronger acid. That's why carbonates are so easy to dissolve- H2CO3 is a very weak acid that can be substituted by almost any other acid and because it is not very stable, it decomposes and creates CO2 bubbles. HCl is a very strong acid but both HCl and HNO3 can be released if H2SO4 is applied on chlorides or nitrates, creating more stable sulfates. If we want to dissolve CaSO4, in a sense no acid can help us. Oxalic acid is one solution but not as an acid but as a complex-forming agent. Oxalic acid binds Ca2+ into a very stable complex, dissolving CaSO4, otherwise very difficult to deal with. At the same time, oxalic acid is poisonous because it binds Ca2+ in live organisms into complexes. Calcium is still present in an organism, but not a necessary free ion but a very stable complex that is useless. Hypocalcemia is induced just like in case of HF poisoning, only due to a different chemical process. Fe oxides in form of rusty crust can be removed by binding Fe into a soluble complex. It is strange that HCl and HNO3 are unable to dissolve a simple oxide of such a metal as iron. The problem is that Fe forms complicated oxides and peroxides that are difficult to attack with regular acids and are thus surprising insoluble. Oxalic acid and oxalates are unstable at higher temperatures and decompose into CO, CO2 and H2O. If there is too much iron oxalate on a specimen that does not go of, it is possible to heat up the mineral (if heat does not destroy the mineral itself), oxalate decomposes and the mineral, with reformed Fe oxides, can be repeatedly treated with oxalic acid. Because of thermodynamic instability of oxalic acid and its salts, one other danger arises. Termal decomposition releases carbon monoxide and this starts occuring once the acid bath boils. Therefore oxalate solutions should be heated carefully and never boiled.

In general, it is important to note that each acid is a solution for a specific problem. There is no universal acid that dissolves everything and each acid is characterized by its specific set of properties. It is also important to note that concentration and temperature may change the acid's properties and abilities to achieve something exrtremely- a few percent off can seem like a totally different substance. Sometimes, acids must be even combined for example to dissolve gold and so on. It is important to know that each acid is usefull but in a different way- and each acid is dangerous but a different way. I ackgnowledge that HF may be the most dangerous but that's because it posesses unique properties that coincidently are not compatible with human body.
Alan Plante August 01, 2006 03:27PM
Sorry about that, Albert...

We are so used to novices showing up here asking about the use of HF that we are pretty much programed to say: "Are you NUTS!" :~}

I'm sure you can appreciate the need for people to be cautious about giving certain types of info to people they don't know - especially when it comes to extremely dangerous things like HF. At one point, Jolyon had one or two people who were using HF, even though they were not trained and didn't have access to a proper lab, telling others here that it was just fine to use it for mineral cleaning, no problem... It was at that point that Jolyon instituted the present policy regarding the discussion of HF here.


Barry Flannery August 01, 2006 03:48PM

'' it not only causes painful burns '' This is untrue, the reason HF is so deadly, it doesn't burn, you don't even feel it until it is busy attacking bones-too deep to clean off with water!

Paul L. Boyer August 02, 2006 02:24AM
There have been excellent overviews given here. Just two more points to mention (in my opinion).

1) As mentioned above, hydochloric acid will release HCl into the air. If you are messing with concentrated acid, even a well ventalated area may not be enough to prevent you from getting a good whiff of the stuff. It burns, baby (I was using 12 Normal HCl). You really need air flow taking fumes away from you, or be sure it is reasonably dilute.

2) An old chemistry lab warning! When diluting acids, add the acid to water. NEVER add water to acid. Mixing water and acid releases heat. If you add acid to water, the heat is absorbed reasonably well by the water. However, if you add water to acid, the acid (being concentrated) will be on the bottom below the water, and the heat released can be enough to launch the water (and acid) right back out of the flask or cylinder. I saw it happen with sulfuric acid with water dumped on top, and we had bad acid rain.
Albert Russ August 02, 2006 07:39AM
You are right, Paul. Actually the results of mixing acid with water vary differently but since sometimes the reaction is so vigorous and sometimes it is not, it's better to follow the same step and pour acid into water for safety reasons. H2SO4 releases lot's of heat when mixed with water but the heat released is verz much dependent on its initial concentration. If close to 100%, pouring water on it would be suicidal because enough heat would be released for the acid to be splashed all over. The same accounts for 80% HNO3 and over. Besides violent reaction with water, lot's of NO2 becomes released. 65% commercial HNO3 usually only heats up if water is added to it, so does HCl but for safety reasons it's better to always add acid to water and even that slowly to avoid any accidents unless you really know what you are doing. Sounds like a chemistry class but good knowledge about acids won't hurt before proceeding to mineral cleaning. I guess I am too freaked out to work with HF after reading all the safety instructions on the internet...
DebS August 03, 2006 03:51PM
I would never use hydrofluoric or sulphuric acid. Ever. It's extremely dangerous.

I have used oxalic acid in dilution to get rid of iron both on minerals and in toilets!

I have also used hydrochloric, a weakened variety sold at hardware stores for calcite, but I HATE even using it. I have always used it outside, never inside. And with a full face shield and in a locked but airy shed. I hope not to use it ever again.
Daniel Russell August 03, 2006 06:21PM

If you will google "hydrofluoric painful burns" you will see numerous citations on the painful burns that can be caused by hydrofluoric acid, including some case studies.
Claus Hedegaard August 04, 2006 10:57PM
Unfortunately too many are too scared of chemicals - 'it will blow up', 'you will from just looking at it' - but I must admit hydrofluoric is one of the relatively few chemicals that make me very cautios (I have letters after my name too, have dealt with large volumes of exotic substances, been in charge of lab security).

I have seen people in developing countries seriously hurt because they have used HF and not known what they work with and I know of numerous mineral dealers who are idiots ... careless idiots.

Fine with me that we do not dispense advise on working with HF as such, but allow my to put forward one piece of advise to those who fail to appreciate HF should not be used except under exceptional circumstances:

If you work with HF always use the gear mentioned in the MSDS, etc. and ALWAYS have a jar of calcium gluconate gel next to where you work. Before opening the HF, you check where that jar is and that the cap is not stuck. If you get HF, however dilute, on your body put on calcium glucionate gel immediately - only rinse if it is a major spill, calcium gluconate gel goes first. The calcium binds the HF and may (MAY!) prevent tissue damage.
When you've done that, then you call the ambulance.

Calcium gluconate gel is readily available in shops dealing in chemicals, safety gear and most pharmacies can get or make it. I have even seen mineral dealers selling it (mail me if you need an address).


Claus Hedegaard
Google me to find me!
Barry Flannery August 12, 2006 11:07AM

Hydrochloric Acid isn't that bad (at least at 10%) as I regularly use it when ever I can get my hands on it...
The only danger is if you spill some when it hasn't been diluted or if you accidently get a whiff of it while pouring but apart from that I find it quite safe but always have a nearby tap and plenty of basic substences ready.

Richard Bielek September 03, 2006 11:19PM
Dear Albert,

our common friend, Mgr. Kusik, has once used HF and since that time his finger is twice bigger. It is up on you to continue playing with hazards but it may happen that your mother will again remove the glaze from your WC. Anyway, I support your scientific approach and I am on your side while cleaning the minerals, including mines, with selected chemicals.
Your friend
Paul L. Boyer September 04, 2006 08:00PM
Here is the material safety data sheet for hydrofluoric acid. This comes from a supplier of fine chemicals. As you can see, they do not view this chemical lightly. I would be using all sorts of protection if I somehow decided to play with this stuff.
Peter Haas September 04, 2006 08:08PM
Particular emphasis should be given to the line: "Skin contact causes serious skin burns WHICH MAY NOT BE IMMEDIATELY APPARENT OR PAINFUL."

Barry was entirely right in saying that you don't feel it when it comes in contact to your skin - unless you get contaminated with a larger volume. The skin burns are the result of a necrosis of the tissue through which HF has penetrated. If you can feel it, it's too late ...
Paolo Malesci September 06, 2006 11:26PM
I believe this is the resume for non-chemist:

1) DON'T USE HF (hydrofluoric acid)!
2) when you use acids use only commercial type and dilute slowly IN water to obtain maximun 10% concentration;
3) use gloves;
4) work in a well ventilated area;
5) have a bucket with sodium bicarbonate solution near you;
6) after this remember that acids are always dangerous (except for 5-7% acetic acid = vinegar).
Pete Nancarrow September 08, 2006 05:27PM
Re Paolo's No 5: I know the comment is well-meant, but without wishing to muddy the water, it is too great a generalisation, and it is simply not true that acids are always dangerous, and it doesn't really help to make people afraid of acids per se. There are many acids apart from vinegar which are considered harmless when compared to strong concentrations of the mineral acids. Several are even drunk by most of us on a regular basis: lemon juice has a pH of about 2.5 due to it's high content of citric acid, and many other fruit juices (even tomato juice) are also acidic; sparkling mineral water is carbonic acid, and of course, Coca-Cola contains both carbonic and phosphoric acid. Each acid should be considered individually, with respect to it's concentration and it's chemistry, and hence it's corrosive potential and toxicity, be it insidious or acute - compare citric, boric, hydrofluoric, and hydrocyanic acids for example.

Having said all that, I concur absolutely that the only sensible advice concerning HF is that unless you are trained in it's use and are intending to use it in a laboratory equipped for it's use, don't even think about it! It's hazards are in a league apart from most of the common acids. Just about the only other compounds I ever worked with which came anywhere close to HF in 'scare factor' were phenol di-iodo arsine and saturated solutions of organic thallium salts.

Pete N.
Pete Nancarrow September 08, 2006 05:29PM
Sorry typo - should be item No.6, not 5
Paolo Malesci September 08, 2006 11:33PM
I think that non-chemist don't know existence of horganic acids, except acetic and oxalic (and perhaps citric and ascorbic).
I know that there are many horganic acids not dangerous and we eat someone very often but I've never seen someone cleaning a mineral with an apple, so is better to talk "acids are always dangerous"; trained peoples know risks and safety procedures for working with dangerous agents, but the others don't.
Alfredo Petrov September 09, 2006 03:03AM
Re "acids are always dangerous": A very large number of collectors use HCl or other acids for cleaning minerals, so trying to frighten them with exaggerated danger warnings is unhelpful. People will use them anyway. Better to use this space to teach them the safe ways of using acids. Society these days seems to be more prejudiced against "science" dangers than it is against many other dangerous activities. When was the last time you saw any campaigns to stop people from skiing, mountain climbing or motorbike riding because these activities are dangerous?
Mess O'Potamia September 09, 2006 03:57AM
hey... Timothy Leary used acid for fifty years and it didn't kill him! If we laid all the people who used acid since the 1960's end-to-end, we'd have... ummm... the US Congress...
Paul L. Boyer September 09, 2006 12:53PM
I agree that people will use acids to clean their minerals, and we should teach them the safe way of using them. However, I think the thrust of the postings are that HF has too narrow a margin of safety to consider playing with. Sulfuric acid, HCl, etc can be worked with in some safety, but HF can kill you in too much of a hurry.
Anders September 11, 2006 03:58PM
I must agree with most of the posts above. I have worked a summer with etching lenses with HF and HF is not for the "common user" as it is way to dangerous and could not be handle safely outside a chemical laboratory. I could only say that even the guys that I was working with regarded it as a extremely nasty chemical and did actually use all the safety precausions all the time... and that was a guy that had been etching glass for most of his life. So my advice is just to stay of HF... even though it unfortunatelly has no good substitutes for disolving quartz and other silicates.

As for the strong inorganic acids (HCl, sulphuric acid), I would say they should be handle with great precausion and in most cases acetic acid or citric acid will give even a better results wich much less "nastyness". However, they are not at all as dangerous as HF.

... well in short stay of the HF
Michael September 28, 2006 05:39PM
Does anyone know if diluting HF down to below 1% makes it sgnificantly safer? We currently use it at 5% and could get it lower,to say <1%, if it made it safer to handle.
Alfredo Petrov September 28, 2006 07:10PM
Michael, if you're going to use it that weak then you may as well use the somewhat safer ammonium bifluoride instead.
Don Saathoff September 29, 2006 05:19AM
And, besides, who's doing the diluting???....You're STILL dealing w/ HF!!!!!
Michael September 29, 2006 11:31AM
Yes, but diluting is a single controlled step, that we can ultimately get our suppliers to do for us. I'd like to get the % concentration down to a level where it could be handled safely, and not worry that a single splash or inhaling any stray fumes would lead to hospitalisation.

I hoped that by increasing the temperature and extending the cycle time, we could get the same result but in a safer way. I think even 0.5% might work.
Michael September 29, 2006 01:49PM
I read that HF is used in car washes, and for cleaning patios. Presumably that means that at some level it becomes relatively safe - mind you - I won't stand near the spray the next time I get my car washed! Does anyone know about this?
Jolyon & Katya Ralph September 29, 2006 04:52PM
Here's an interesting article about the use of HF in carwashes...
Don Saathoff September 29, 2006 09:49PM
Ammonium BiFluoride will do the same job under the same conditiond as diluted HF.....with a fraction of the danger!!!
Dominik Schläfli September 30, 2006 08:14PM
Jolyon, don't forget the article is from january 1999.
Rick Kennedy October 06, 2006 05:50PM
The use of HF on cars, as described in the article, is truly frightening. Regardless of what it does to the cars (I'm not qualified to say), having drums of HF at any concentration high enough to be useful around people who are not trained chemists or chemical workers is a dangerous situation. Please don't take this usage as proof that "you too can do this at home." I can only hope that things have improved in the car wash industry since 1999.

I do have experience with HF, having worked at a research and manufacturing facility where we used truckloads (many of them) of 70% HF. We could not get near HF above a few percent without full acid gear on -- double gloves, apron or acid suit, rubber boots, face shield, respirator. HF exposures were rare and minor, so I do believe HF can be safely and effectively used, like any other dangerous chemical. However, it takes a world-class safety program, which we had. Your typical car wash does not.

A note of clarification about painful vs. not painful burns. HF burns are reportedly extremely painful if the acid is concentrated, say 50% or more. Below 20%, the HF is still extremely dangerous but the exposure is not painful until maybe 24 hours later. So a worker may think it was just water that splashed him, and then 24 hours later when the area becomes red and painful he may not even remember what caused it, and neglect to get the proper treatment.

Lastly, about diluting to a "safe" concentration... I would venture that any concentration high enough to be useful is still dangerous.

Rock Currier June 17, 2007 08:56PM
By this time you have probably already done some HF/Quartz experiments. If not I’ll tell you that it takes a long time to do more than just etch the surface of quartz and for the first few hours it seems to do almost nothing, even concentrated material. My experience has been that it will not leave your quartz with a lustrous 'polished' exterior like it will leave on glass. I think there is too much fear mongering on this site about the use of strong acids and not enough balanced informed discussion.
G. Evans April 10, 2008 02:41PM
As a qualified Inorganic/Organic chemist (BSc/PhD) I find the whole discussion on the use of acid very pedestrian. What I could tell you about the cleaning products you find under the kitchen sink would scare the pants off you, and most would make go down to the local stream to wash by beating their clothes against a tree. Every chemical based substance you can buy at the supermarket, petrol station or drug store has the potential to cause great harm. As a chemist, now retired, I lived with these risks every day and used substances more lethal than the common mineral acids. Most kids get to use hydrochloric, nitric and sulphuric acid by the first year of senior high. The issue is reasonable risk and safety. Use gloves, safety glasses and a well-ventilated area. Do a web search on undergraduate chemistry courses, most Universities have lots of practical info available for download, consult a text like Vogel and go and speak to the Science teacher at the local high school. Can I guarantee that all will go well, well of course not, no more than when I say goodbye to the wife when she goes shopping - accidents do happen, common sense and knowledge will always help to minimize the risks.
Mark & Linda Mahlum April 14, 2008 03:57AM
What about ammonium bifluoride? I have crystals of hubnerite coated with quartz that would be quite attractive if the quartz could be removed. What safety precautions should be used with this chemical? How effective is it? Will it remove kaolinite? Will it dull the quartz crystals?

Any help would be appreciated.

Rock Currier April 15, 2008 09:19AM
If the coating of quartz on your hebnerite is very thin, ammonium bifluoride may do the cleaning you desire, but if it is of any thickness you will need to consider that perhaps only hydrofluoric acid will clean it properly. Most if not all of the hubnerite specimens from the Adams mine have been treated in HF to remove the natural quartz coating. Also most of the twinned ferberites from the San Cristobal mine in Peru, have also been treated in this fashion. I don't think you are going to find anyone on the board here willing to discuss the use of this acid for cleaning with you on line. If you can demonstrate that you know something about chemicals and proper safety procedures, contact them off the list and make a good clear case of what you want to do, I think there may be knowledgeable people here that may be willing to discuss it with you. The liability issues are considerable.
Mark & Linda Mahlum April 16, 2008 03:27AM

I'm neither qualified nor equipped to work with HF. That's the reason for my interest in ammonium bifluoride. I have some amethyst scepters with a coating of some kind of thin, but dulling silicate that would benefit from a cleaning in addition to my hubnerite. Additionally, I have some quartz after calcite rhombs to six inches that are coated with something that dulls them. Maybe. They may be etched by Hf from dissloved fluorite in that vein, I'm not sure. Trying ammonium bifluoride can't hurt. But what are the safety ramifications. I live at the end of the road in the San Juan Mountain foothills with plenty of open space, for what that's worth.

Paul L. Boyer April 16, 2008 04:11AM
Open space is not the issue here. It is what HF can do to a person's body in very short order. Proper equipment and training is needed to be sure you aren't an EX-mineral collector.
David Von Bargen April 16, 2008 01:51PM
Ammonium bifluoride isn't much safer than HF. See MSDS (especially Potential Health Effects):
Jesse Fisher April 16, 2008 03:58PM
Fluorine ions are not referred to as the "Tiger of Chemistry" without reason. Fluorine in it's free state is EXTREMELY reactive and anything that provides it has the potential to severely damage human tissue. The insidious thing about the process is that one is one aware of the exposure until after the damage has been done. Even if you don't manage to hurt yourself, if you do not understand the chemical reactions involved with what you are doing, there's a very good chance you could damage or destroy your specimen in the process.

In actuality, most coatings on mineral specimens are best removed by mechanical means, i.e.: an air abrassive unit. Yes, they cost money, but what is your health and safety worth? Unless someone is an experienced laboratory chemist, I would strongly recommend staying away from chemical cleaning and investing the money on one, or paying someone who has one to clean your minerals for you. A less expensive, thouth not nearly as effective alternative is a high pressure water gun.
Tom Eden September 21, 2008 12:01PM
My problem is that I have gold jewelry which is not marked to identify its K.
I'd like to seperate the gold from its accompanying alloys (if any) and was told to
soak it in HNo3 for about a week. I was told the HNo3 would dissolve everything
except the gold. Is it really that simple? Or is there other things involved?
NH September 21, 2008 06:23PM
The alloying elements used in gold jewelry are all soluble in nitric acid. However, if the gold is reasonably pure, the metals on the outside might dissolve without leaving enough pores for the acid to reach the inside, and so it might take a really long time to remove all of the other stuff. If there is not a lot of gold, I would imagine that this method would work well: a similar process is used to make Raney nickel from a nickel-aluminum alloy.

One common method (Wohlwill process) of purifying gold is electrolytic, but you need pretty pure gold to start with, and gold chloride for the electrolyte.

I found a patent describing an electrolytic process using ammonium chloride as the electrolyte. If it works, this seems like the best method.

With either dissolving or electrolytic methods, the gold that you get out will be finely divided (powder) rather than a solid mass. In either case, you might also want to consider reprocessing the solution to recover silver and (if you process white gold) palladium. Silver can easily be removed as the chloride with the addition of sodium chloride solution or hydrochloric acid (remove the gold before adding any chloride, or you will get aqua regia, which will eat the gold; adding chloride will also precipitate lead, but this shouldn't be present to any large degree).

You might also consider cuppelation - a method that involves blowing chlorine gas over molten gold is used industrially, but would obviously be very dangerous and nearly impossible to do without specialized equipment.
Rock Currier September 25, 2008 09:21AM
Thought you description of the various acids was quite good. Why don't you turn it into an article that we could post in the sticky message at the top of the Cleaning bulletin board? My experience in using HF on cleaning specimens is not extensive, but I will be glad to share what I know off line.

Rock Currier
Crystals not pistols.
Miko January 02, 2009 05:10PM
Albeit an amateur mineralogist, I have a persistent question regarding the nature of this particular thread.

What is the motivation behind all the authors who insist on publishing their own sometimes rational, sometimes irrational fears, INSTEAD of answering the original question, which had to do with

*) How to properly or effectively use HF in the structural & artistic transformation of Silicon Dioxide in the form of Quartz?

It seems obvious to me, and perhaps the original author, that HF is available to whomever seeks to find it. That being the case, it seems that one stern warning is enough, and I have faith enough in OSHA labels that this warning is already apparent to the buyer.

So do I really need 75 or more posts telling me about the dangers, some real and some made-up?

Sharing a humorous tale from my childhood - My sister was a chemistry professor when I was a child. I quickly, through charm enough of my own, grew to be very adored in the lab where she worked. The chemistry director befriended me especially when I said I always wanted a chemistry set for christmas. Instead of a lousy rusty-boxed set, I ended up receiving lab chemicals from the department, in boxes. I remember, probably to the ghastly vehemence of most of the fishwife posters here, playing with hydrochloric acid, sulfuric acid, ferrous cyanide, mercury (yes, the shiny liquid metal), along with countless others. The most delightful, now that I read this entire board, yes, was the infamous 'HF.' I'm not denying that I may be alive for very miraculous causes, however, I sit here wondering how many of the authors realize that one warning is enough.

I enjoy the memories from my past, I enjoy remembering the conversations I had with very intelligent and kind professors who taught the dangers as well as the beauties of science, so that I didn't act afraid, but was taught to think and act responsibly.

If you ever remember being a child, explaining what you know about a subject may prove the more appealing offering. One plays with minerals from curiosity, and even though some cats have unfortunate experiences, it seems like the original authors on this board are seeking to temper their curiosity with knowledge, not fear.

Franz Neuhold January 02, 2009 06:09PM
Dear Miko!

Yes, we need 75 or maybe more posts on this issue. Your post is an example for irresponsibility and arrogance, which can be misleading and very dangerous for other inexperienced people. Your main argument is that you are not dead. This does not convince me.

In my opinion it is careless and stupid to give HF to a child or use it outside a lab with the necessary facilities.

Best regards,
Daniel Russell January 02, 2009 06:17PM
Perhaps it is because not everyone who wants to use HF to etch stuff out of quartz has a background in chemistry, nor toxicology, nor hazmat response, and especially because not everyone reads the included Material Safety Data Sheet (or can understand it).

If you wish to get nekked and roll around in plutonium, feel free. My ethical obligation (if any) ends with pointing out that its probably a very imprudent think to do. However, if I explain to you how to get plutonium, or how to roll around it in, the current legal climate can result in my facing potentially serious legal consequences. (I ain't saying its right, I'm just saying its so. I much prefer the simpler logic of Natural Selection... anyone who wishes to get their Darwin Award, the line forms on the right! Apply early, and apply often!)

You say "If you ever remember being a child, explaining what you know about a subject may prove the more appealing offering." This is precisely why harping on the safety issue involved in HF is important.
Claus Hedegaard January 02, 2009 11:44PM

> I'm neither qualified nor equipped to work with
> HF. That's the reason for my interest in ammonium
> bifluoride.

You need to take the same precautions with ammonium bifluoride as you do with hydrofluoric acid. Ammonium bifluoride is less reactive and less prone to produce fumes, but perfectly capable of causing tissue damage. I believe Rock is right and that this boards suffers of too much fear mongering with respect to chemistry.
But you do the right thing, ask for advice, when you don't know. Until you have a good understanding of chemistry and working experience with other chemicals, I recommend you for not use hydrofluoric acid, nor ammonium bifluoride.

That said, both have their proper use but more often than not, specimens are ruined. When you visit mineral shows, you invariably see Chinese and (particularly some years ago) Pakistani & Afghan specimens that got the good old hydrofluoric acid rinse ... and were completely ruined.

All the best


Claus Hedegaard
Google me to find me!
Alysson Rowan January 03, 2009 10:33PM
When I worked for a manufacturer of clinical analysers, we routinely needed to etch the glass membrane of one of the ion-selective electrode assemblies. The reagent used was a mixture of an acid and a fluoride (and no, I'm not saying which). The concentration was the lowest that would do the job and the bottle size (150ml) was calculated to be less than the F25 for adult human (i.e. consumption of the bottle would kill less than 1 in 4 people).

Shall we say that I have a healthy respect for any soluble fluorides.

When you invited me to see your etchings, I didn't expect to
see so much degraded quartz. Really.
Alfredo Petrov March 22, 2009 12:38AM

In household detergents? One hopes they are combining it with something else to make a final compound other than HF but, in that case, why not do it at the source, to eliminate the need for moving tons of HF along the public roads?
Peter Haas March 27, 2009 01:43PM
"Whoever believes in everything he's reading should better stop reading at all."

A newspaper article is certainly not the best source to learn something about chemistry. Whatever they wanted to say, they screwed it up.

It is true that HF is used as a raw material in the synthesis of particular surfactants (perfluorinated surfactants). Surfactants, on the other hand, are used in a whole array of different products, among which also are household detergents (note that a detergent is defined as a formulation that contains a surfactant). It is not true, however, that these particular surfactants are used in household detergents. Perfluorinated surfactants are chemically extremely stable and that there is no risk of setting fluoride free in normal use (deliberately burning them would not be a good idea, though). They are toxic, but for different reasons.
So, if you google for products that are manufactured from HF, you may find surfactants. If you google for the applications of surfactants, you probably find household detergents. Linking one to the other may appear logical (well, logics again !) if you don't know that "surfactant" is not a chemical classsifier but just refers to an obscure physico-chemical property that is met by hundreds of thousands of molecules.

HF is also used to produce hexafluorosilicate 2-, which may be used as a disinfectant. Again, hexafluorosilicates are very stable compounds.
Rodrickez August 17, 2010 10:09PM
I need the complete process of Chemically polishing Quartz crystals, If somebody have the complete process of chemically polish quartz crystals with ,please share it with ammonium bifluoride me.The ratio of mixing ammonium bifluoride with distilled water.
Alfredo Petrov August 17, 2010 10:47PM
If this polishing you want to do is related to the problem you reported in your other post (ie. lost luster on quartz crystals by overcleaning with HF), then using ammonium bifluoride will only exacerbate your problem, because NH4-bifluoride attacks quartz the same way HF does, just more slowly. Too bad that you ruined the quartz with HF, but that quartz is going to stay ruined; can't put spilled milk back into the bottle.

Edited 1 time(s). Last edit at 08/17/2010 10:48PM by Alfredo Petrov.
Anonymous User August 18, 2010 03:48AM
Hi all!

Albert,even if you (obviously) are an experienced scientist,you'd better not use it.

I will answer randomly,since many replies are present.

HF burns can be noticed immediately or after a while.The burns are still burns,however,the acid,by absorbing Calcium can attack the neural system and thus the brain cannot realize the pain.

This is very dangerous,since the therapy is delayed.

Calcium gluconate gel is not enough in most case.One needs pills or even injections.It depends on the skin surface attacked.Gel is better than nothing,but not enough.

From my personal experience:

I have a couple of friends who used to use the acid.One of them used to use it with bare hands and no mask.He never had burns dipping his hand to the elbows inside the solution.He suffers from heart failure (probably due to the acid).He has been a miner and a person always living at a fresh air mountain site with healthy food and lifestyle.

The other one used to use gloves but no mask.He didn't notice the glove had a hole and he lost tissue to the bone of his finger.The doctors treated well the necrosis and the tissue was restored.However,no calcium gluconate was applied and he will have some organ failure in the future.

Note that both of them lead a perfect lifestyle!A smoker junk food eater with an office job will have much more serious problems!

Even if an accident doesn't occur,improper equipment will allow the acid to penetrate the skin and lungs and will cause health problem in the future!

All this for removing Quartz.

Even thinking financially,the use of the acid can provide you a good specimen that would be as expensive as 10.000 USD maybe?A laboratory can do it for you for some hundreds of USD.

An accident will cause you health problems that eventually will cost you much more!

I'm not sure if it right not to provide information on using the acid.There are people who won't believe until it happens to them and will use the acid.

Now,Albert,what do you mean by getting an interesting structure?seen specimens treated to remove a second generation and reveal the crystal color,but have you seen the result?Removing Quartz off Quartz?

You say you want to etch to get interesting structure.Do you want to get an etched crystal?What for?

With just a dip in low concentration (2-3 %? I have no idea) you will get the outer surface of the crystal with a look of surface cracking.

This is a fake to me.Removing Quartz off some other species would be ok,but Quartz off Quartz means both generations or crystals will be affected so this as valuable as polished specimen and even uglier!

Please post a photo,so we could understand what you intend to do.

Dan Fountain August 18, 2010 01:07PM
I have a copper crystal group with a crust of what appears to be prehnite covering it. I previously requested information about the interaction of HF with copper and prehnite - will it remove the prehnite? Will it etch the copper? I received numerous warnings about the dangers of HF, but no information of its interactions with the minerals. While I appreciate the warnings, I work in a facility where we use HF as a de-scaler in an automated anodizing line, so safe handling and use of the chemical is standard operating procedure. I would not be using the chemical myself; I would leave that to the guys who do it every day. The questions remain: Will HF remove the prehnite? Will it etch the copper? Thanks in advance for any information you might offer.
David Von Bargen August 18, 2010 02:33PM
From some of the literature it appears that there will be some solution of the copper (and possible redeposition forming masks) that is also influenced by how oxidizing the solution is. I would guess that you would end up with a pretty "bright" copper, not unlike that when you etch a sample with HCl.
Dan Fountain August 18, 2010 02:42PM

Thank you for the reference!

Donald Peck August 18, 2010 04:30PM
The most vulnerable portions of the body to acids are the eyes. Even to dilute acids! ALWAYS wear safety glasses (preferably splash proof goggles) when working with acids!. If any acid splashes into the eyes, rinse with running cool water for at least 10 minutes (You will need help, as you will be unable to hold your eye open.) and then get to a doctor - - fast.
Jolyon & Katya Ralph August 18, 2010 05:04PM
The only advice we give about HF on is DO NOT, EVER, USE IT.

If you are trained well and are carrying out work with the appropriate safety gear and equipment, even then we wouldn't advise you go near the stuff!

Rock Currier August 19, 2010 03:14AM
I have used HF over a period of time to remove quartz from Michigan copper and silver specimens. It may etch them a bit, but I am not sure about that. At any event, the results that I got I felt were well worth the effort, but again, unless you know how to work with acid, my advice is also not to do it.

Rock Currier
Crystals not pistols.
Ryan Eagle August 19, 2010 02:45PM
During my time working in Mount Isa, I was trained in the use of HF. There, it is used to prepare rocks for the detection of what we called tuffaceous marker beds, continuous k-feldspar rich layers within the siltstone containing the orebodies, which could be used to define the rocks' stratigraphic position. The issue with these TMBs is that they are hard to visually identify. Thus, HF is used to prepare the suspect rock before a stain is applied. If the stain sticks, then you are likely looking at a TMB. This was a reasonably routine procedure during core logging and pit mapping. The safety gear required to handle the HF safely deserves no less description than being the equivalent of a space suit. It really isn't worth the trouble unless you need to use it for commercial mineral preparation, or are doing something worthwhile as far as the science goes. In the latter case, it's probably better to give the work to someone who has dealt with HF before.
Jeffrey Rank August 31, 2010 05:38AM
I agree with rock currior. gotta know your shit! and it really only comes with trial and error. gotta learn what will do what with acids, personally I work with fine chisels, a dremal and diamond and carbide tips to achieve its natural condition. but certain acids at times to achieve a result. either way, its an art!
David Von Bargen August 31, 2010 10:41AM
Well, the only problem with trial and error experience is that with something like HF, it can leave you very dead.
John Betts August 31, 2010 05:12PM
I have successfully used hydrofluoric acid diluted to 3% and find that 4 hours at that strength softens most feldspar, dissolves pocket clay, and just starts to attack quartz. I have also used ammonium bifluorite for similar problems.

The smoky quartz from the Smoky Bear Claim, New Mexico were all treated with HF/ammonium bifluorite in sequence to remove the outer quartz crust and maintain luster. Novices tend to oversoak these in the HF, resulting in telltale white cracks where the HF penetrated "burning" the quartz.

John Betts
Alfredo Petrov August 31, 2010 05:46PM
Most wolframites from Bolivia have been cleaned with HF; nothing else seems to do the job. I use it as a last resort, with fear and trepidation, and great care, outdoors.
Peter Andresen August 31, 2010 08:31PM
Before getting close to HF make sure to have a neutrilising-gel tube next to you! If an accident happens it might save your life. Unfortunatly I don't remember brands or names, but it was always next to the rescue-shower in the lab at university when I studdied...

Personaly, I'll never bring HF to my home, NEVER!
Alfredo Petrov August 31, 2010 09:05PM in California sells the calcium gluconate gel. They mail it worldwide.
Tim Schafer April 06, 2012 10:17PM
I was searching for a method of dissolving quartz sands from super-fine gold concentrates, when HF popped up as the only real solution. Then I read the MSDS. Back to the drawing board. I came across the Igoli merecury-free extraction. Using pool acid and bleach 1:1 to dissolve, and sodium metabisulphate to precipitate the gold after filtering. When done correctly, this should make for a very eco-friendly, and productive reclamation technique for the small scale mine operator. Being that I am not a chemist, and would like very much to maintain still alive status, not offend my neighbors, and stay out of court, I would like to ask for some direction from people who know.
How difficult is it to set up a scrubber for the chlorine gas in a home lab, and what would I need? I have seen some pictures, and a couple in person, but these are large scale scrubbers at chip plants. Any advice, and or direction WILL be greatly appreciated.
I have stumbled upon a very sweet find, but the gold is so fine that mercury amalgamation is just not possible efficiently. The make-up appears to be quartz, alot of calcium (numerous caverns in the area), ridiculous amounts of mica, gold, visible copper and silver, and magnetics. I hope I have not violated your sacred forum with such queeries. Have a fantastic day!
Alfredo Petrov April 07, 2012 03:28AM
Mercury is much safer and easier than what you are proposing. Use a retort to recover the mercury and all will be well. :)-D
Jenna Mast April 07, 2012 10:58PM
The semiconductor foundry at school uses HF.
They're quite fortunate to be across the street from the hospital!
Tim Schafer April 11, 2012 05:47AM
Your response is appreciated Mr. Petrov, and your concerrns are noted, but mercury is ineffective as the gold is just so fine and flat tthat Hg simply rolls right over it. I used mercury first, and recovered some, but only a very small percentage. A scrubber just does'nt seem too extreme. Please indulge me.
John Lindell April 11, 2012 09:22AM
Albert, I have used both HFl and ammonium bifluoride on quartz and would recommend the latter as the reaction is slower and easier to control. HFl can frost quartz rather quickly. It is good for removing quartz from fluorite or etching gold out of quartz, but is harder to judge when removing silica scale or secondary growth off quartz crystals. It is also dangerous because you don't feel it burn like other acids as it is very penetrating and will damage nerve endings without pain. My wife was wearing rubber gloves using HFl while processing some Bessemer pseudomorphs 25 years ago and didn't notice the pin hole in one glove. She ended up with a very nasty ulcer on her hand. The Ammonium bifluoride is the same radical in solution, but especially when used cold is excellect for removing opaline scale or secondary growth off quartz crystals. You can monitor the progress and decide when to stop. It will slowly attack feldspars and other associations so as usual work with test pieces first, pull samples and let them dry periodically to see dry results and be patient.

Edited 1 time(s). Last edit at 04/11/2012 09:24AM by John Lindell.
Alfredo Petrov April 11, 2012 01:04PM
Tim, another option for your consideration: Instead of dissolving the quartz in HF, how about dissolving the gold in aqua regia? Since the quantity of gold is, I imagine, less than the quantity of quartz, you'd need less acid. Quartz will not dissolve in aqua regia.
Rock Currier April 11, 2012 01:05PM
We have a policy here on mindat not to tell people how to use HF because it is so dangerous. So unless you know how to work with this dangerous reagents we strongly discourage its use. Also it is pretty expensive. To buy a gallon of the stuff you will probably have to pay ninety dollars or more. Smaller quantities are proportionally more expensive per ml. If you really feel you have to work with this reagent you should find an old chemist or someone that has used it before and get them to help you and make sure you have all the safety equipment you need to work with it. If your gold is really fine and there is not much of it, it is possible that the acid might cost you more than the value of the gold you recover.

Rock Currier
Crystals not pistols.
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