Hi pmh232,

You don't have to be "daunted". I think we are all here to learn and of course I am willing to share my knowledge as well.

Yes, I have worked years on colloids and tried to synthesizes opals (and other so-called opaline materials).

For opals I have used the common route by synthesizing spherical silica-particles and simply by sedimentation they ordered into a three-dimensional array with play-of-color.
But I could not achieve a final, mechanical stable sample.
For this some expensive devices are necessary and I had no access to it (critical-point-dryer, hot-isostatic-pressing machine . . .
The samples I could prepare were milky-white and extremely porous synthetic opals (like hydrophanes), very brittle.

But I have got the information that another method would be also possible. There natural occuring knobbies (or potch without play-of-color) are grinded down to fine clay and afterwards with acid and hydrogene peroxide the clay is turned into opal. I don't understand the process.
This could be the method "Len Cram" used for his experiments in the Australian outback, I'm not sure.

Maybe you (or any other opalholic) know more?


For those of you, who are interested, here are some links and literature:

For the preparation of monodisperse spherical particles I used the famous Stoeber-Method (with modifications to increase the yield):

Stöber, W. and A. Fink (1968): "Controlled Growth Of Monodisperse Silica Spheres In The Micron Size Range", Journal of Colloid & Interface Science 26, 62-69.

Highly monodisperse silica-sphere are also commercial available, but very expensive. For this reason  I have tried to use cheaper silica-spheres supplied by "Fiber Optic Center ". Unfortunately these particles were not as uniform as promised (very broad size distribution) and not suited for synthesis of opals.

Maybe another company is a new startup from US - "NanoGiant ". If anyone has some more information about their particles, I really appreciate it.


A detailed description how to prepare synthetic opals was published by some Russian scientists:

Filin, S. V., Puzynin, A.I. Samoilov, V.N. (2002): "Some Aspects of Precious Opal Synthesis", Australian Gemmologist 21, 278-282.

This articles can is online available on the homepage of the "Australian Gemmologist":

http://www.australiangemmologist.com.au/opalsynth.html 

In the meantime several patents were applied about synthesis of opals. Among them the most famous of the "CSIRO":

OPALINE MATERIALS (CSIRO, 1964)

and from Darragh & Gaskin:

OPALINE MATERIALS AND METHOD OF PREPARATION

About the origin of natural opals I know only one article:

Darragh, P. J., A. J. Gaskin, et al. (1966): "Origin of Precious Opal", Nature 209 (5018), 13-16.


Now I'm looking forward to some contributions......

Kind greetings

Roy Goldberg

Pinfire - Gems & Colloids