What is a real definition of the % of depth of any color stone ?

I am just curious about "depth".

It seems to me when the stones are light -- say clear quartz, light agua, blue topaz, or white topaz ..

When stones are clear --- the shallow cut -- or less depth seems to have less effect of the stones reflection ..

Any one .. I know there are a huge forumla out there - such as the depth and its % over the larger side, or shallow side ..

Does anyone has any more tips -- on this -- light stones , light color stones -- say even clear quartz ..

Thanks

I am a bit confused by the wording, Paul. Are you referring to facetter's guides of percentage of depth of stone vs width based on the type of stone, ie a guide to proper proportions for cutting to get maximum return of light back through the table, OR are you referring to depth of colour???

It seems to me, for a while, many of the commercial gem cutters had been following the depth percentage of any gems - in the use of that 60% depth of the table --- where yes, for most of the light color stones, that 60% seems a bit shallow and that is good .. But in other stones, in my experience, in the commercial cutting of amethyst and even topaz -- when the depth is increased -- and we have to incresed in some of the cases with amethyst from Irai -- to hold color -- more so when these gems from the region of Rio Grande do sul , their particular zoning requires a more keen orientation to place the heavier "zone" toward the culet to bring out most of the colors.

I am not gemologist nor a cutting expert -- but just have enough keen sense to see how dark tourmalines can be lightened by cutting the stone a bit shallower.

I am merely scouting a bit more -- seeking more common sense cutters -- and see if I can find an echo in here.

Thank you for the reply

Paul,

This doesn't really address your question, but. I've harped endlessly on this website about terminology. It may seen very picky, but people say "clear" when meaning colorless, but actually are saying transparent. Other times people say "white" when actually meaning colorless. When talking about colorless, AND transparent, I prefer the industrial term "water white".

Clear,colorless,white,and transparent are not the same thing.

I will now get off my soapbox.


Don (Peck), am I getting too picky, or too old?

Paul,

Any colored gemstone has a "critical angle" at which to be cut for the best refraction of light it can produce. Dark stones can be cut shallower to increase lightness (i.e. better color) while lightly colored stones are often cut too deep to set to make them appear a richer tone. Various cutters and cutting centers find their own favorite system of angles to best work their rough. There is no chart or formula other than the critical angles. It is more of an art than a science at the point of chosing the cut.
Hope this helps,

Gary

P.S. to Don,
Yes and yes :>}

Gary, I guess I am always have use my intuitive sense along with the best studied and better analyzed documents possible. Since we have cut many of the commercial grade in these past thirty years -- from the horrible cut to retain weight in Brazil to now the better trained/better educated Asians in Thailand and in China to balance out the past and the present.

My link to the industry is by far more of the multi-cultural exposure that have me excited -- Such as in Thailand, upon our final color pick of ruby, we generally use a local Thai lady to see for the color in what red -- or commercial red for the European, for the Japanese and for the Chinese ..etc . Because that slight pink will turn the many Japanese off (in the old days when Japan was a client ) to then the pick of the color based on ethnic preference.

Indeed, the reasons for us to be in this business is that the on going learning, research is just fascinating and often too fascinating when it is mixed with other "human stupidity" -- as in the naming of "paraiba tourmaline" with the presence of copper as being one of those few factors.

Again, I have enjoyed your frank language and if I can be of any help on my end in Brazil and in China . I will love to reciprocate -- After thirty years in t his business - I guess I have seen as many horse's behind - almost as many as the many so called academic with faces not so much different than the back side of any donkey or horse ... in fact, many are just all looked too similar ..

Well, I bit of sarcarsm is healthy for all -- In view of the last years fiasco with GIA and the influence of gem lab influence.. That is just another one of those horses butt scenarios that get me annoyed

Have a good day