How do you make synthetic opal?

[TalonD]

I found this simplified Stober method and was wondering if you chemists out there could comment on whether this would work or not to produce a difracting layer of opal?

Also wondering if such chemicals as TEOS could be obtained by me (an average non chemist) so I could try making some opal in my home lab? If so, then where could I get some? and would household amonia work vs. anhydrous amonia?



For the first solution
Add 12-17 parts of tetraethyl orthosilicate (TEOS) to 100
parts of alcohol (ethanol) with stirring.

For the second solution
Add 30-50 parts of ammonium hydroxide to 250 parts of alcohol.

Next:
Add the TEOS/alcohol solution to the ammonia/alcohol solution slowly with
stirring. Continue stirring for about an hour to allow the reaction to come to completion. Depending on the exact concentrations of reagents you will generate a milky suspension of 250-400 nanometer silica spheres. Pour the suspension into a tube and allow it to settle. A thin layer of opal color will form in a few days and within 2-3 weeks all the suspension will have settled out and formed a brightly diffracting layer of "opal" usually a few millimeters thick depending on how much solution and the size and shape of the container. You can continue to make new batches and add to the container to increase the thickness of the growing opal layer.

 

[TalonD]

I see no one has responded yet, but.. I just found a source for some TEOS.

 

[lightarrow]

I see no one has responded yet, but.. I just found a source for some TEOS.

I think you haven't get answeres because it's a very specialistic subject. About me, I had never heard of tetraethyl orthosilicate before.

 

[TalonD]

I thought this sol gel process might be commonly known in the chemistry forums.
But I've found lots of good info by looking up sol gel and nano particles. TEOS has lots of acronyms so you might know it by another name perhaps.

 

[artpty]

Hi TalonD, have you made any opal yet?
im very interested to see how you went...

 

[TalonD]

Hi
I didn't make any yet. I would like to try it sometime but have too many other irons in the fire.

 

[Cuauhtemoc]

Well, about the ammonia, it doesn't specify the concentration, but since it's ammonium hydroxide(anhydrous ammonia would be a gas at room temp) it's certainly ammonia in water,just like household ammonia, if household will suffice is hard to say, because it's normally pretty diluted.

 

[chemisttree]

I've never seen the process used without some surfactant. It will be interesting to see if the result is monodisperse. I don't think it will make monodisperse sol gel without the surfactant but that's left for you to determine.

 

[PMH]

TalonD, I have made synthetic opal(ine material - ie: not hardened) using a process similar to the one you give.

I used TEOS, reagent-grade ammonia, reagent-grade alcohol (denatured, I think), and super clean water ("triple distilled" or some such).

I have not tried it with ~store grade~ products, but my source says that the slightest impurities will screw things up.

I gave away most of what I've made to a friend who helped me amass the required tools.
(magnetic stirrer with stirring rods, ~chemist's stand~ with several arms and adjustable jaws, test tubes, pipettes, etc.)

The process results in a monodisperse suspension that's stable (once the ammonia has been removed) as far as I know. It will coat any glass vessel that it's put into briefly with a whitish coating that makes precious-opal-like (except for the flashes) colors in the sun.

I can't say how robust my process is, since I haven't tried it enough times.

I can say that doing anything stupid will result in failure. Once I left the cover off while it was stirring, allowing the ammonia to evaporate: no good; once I poured the initially-yielded liquid (still strong with ammonia) into a long plastic tube for settling: immediate crash, as the liquid dissolved the plastic.

The best result I've had is a thin band of precious-opal-like fire in a test tube.
...but that's good enough for me

I haven't yet tried to control the resulting fire color(s).
(by altering the reagent proportions or varying the time that's spent allowing the shperes to grow)

Not to try indoors! The ammonia is nasty!

 

[peterson1972]

i heard that it needs professional tool to produce in Lab. I saw this Synthetic opal in a Hong Kong Jewelry show, I bought a small piece of sample for record.

And I google it, I found this may help,
Chemical Composition: SiO2.nH2O+Resin (Natural:SiO2.nH2O)
Hardness: 4 (Natural: 5.5)
Specific Gravity: 1.80-1.90 (Natural:1.98-2.20)
Heat Resistance: 130 degree C.(Natural:100 degree C.)
(copy from link deleted, you can easily google it)

They use some Resin into it, so it is not feeling very "Stone".

 

[PMH]

peterson1972,

It's not clear what you're saying (that you heard) needs professional tools.

I'm doing it w/ just:

• 
  some glassware (flasks, beakers, pipettes) (optional)

• 
  a magnetic stirrer (really do need something like this - although I've seen people make them from fish-tank aerators)

• 
  very pure reagents (necessary)

The "syntheic" opal you bought would have been labeled "simulant" by an honest dealer; "synthetic" is properly used only for manmade materials that are ... (something like) ... substantially the same as the natural version (in this case, only silica and - maybe - water).