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Techniques for CollectorsAfghanite, is afghanite soluble in muratic acid???

14th Nov 2010 03:40 UTCKristopher Dingfield

Just curious though I guess I could find out on my own. has anyone tried cleaning or removing the matrix with acid?

14th Nov 2010 09:33 UTCMark Wrigley Expert

You can see lots of acid cleaned afghanite and lapis/lazurite specimens online.

Yes acid will "fizz" away the marble/calcite matrix - but really roughs up the surfaces of the exposed minerals, especially if partly included with calcite.

This is done to make a better colour on poorer specimens.

The best prepared sharply defined specimens are usually "mined" out of the matrix.

Cheers

Mark W

14th Nov 2010 11:00 UTCIbrahim Jameel Expert

To emphasize what Mark said: yes.

Usually you can spot the acid washed specimens because they will have rough surfaces that look like they have been coated with a thin layer of white powder. Be aware of oiled specimens though-- when a lazurite or afghanite has been damaged by acid, some dealers like to coat them with oil to bring back the deep blue color.

The proper way to use acid is to coat the crystals with wax first, but unfortunately as the acid eats away at the matrix, space is created that allows the acid to contact the crystal.

The best way is to use physical means only... an electric masonry wheel works best. As mark says, the best specimens have been "mined" out of matrix... often at least 30% more of the crystal can be exposed with a few minutes of work.

I should also point out that that there are different grades of marble that comprise the matrixes. Some are easier to work than others. The semi-translucent, slightly grayish variety is the worst... I'm guessing it has undergone further metamorphosis, so it is harder, less crumbly (to a masonry bit) and really sticks to the crystals.... those are best left alone.

ibrahim