Author Topic: Chalcedony  (Read 2107 times)


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« on: January 25, 2019, 10:26:46 PM »
This batch is discussed a bit in the introduction of my batch calculator:

The basis is this unoxidized glass with a bit of alumina in the form of 3 lbs feldspar.

Silica 47.42 lbs
Soda Ash 15.21
Lime Hydrate 6.78
Potassium Carb 3.94
Borax 5 mole 1.65
Feldspar (custer) 3.0

BTW: If you would rather use whiting, remember this conversion.
Lime hydrate is 74.093 g/mol formula weight. It's molecular formula is Ca(OH)2 so there is one calcium atom per molecule.
Calcium Carbonate (whiting) is 100.0869 g/mol and similarly it has a single calcium atom per molecule (CaCO3).

To make a molar equivalent calculation, I do the following:

mol/74.093g x 453.6g/1lb x 6.78lb = 41.05 mol Lime Hydrate so we just need 41.05 mol of Whiting

41.05 mol x 100.087g/mol x 1lb/453.6g = 9.17lb Whiting!

For a 10 lb Chalcedony batch add the following:
9 lbs of above
Black tin oxide: 2g*
Zinc Oxide: 30g
Iron Oxide: 2g
Silver Nitrate: 4.5g
extra soda ash: 7g

I really like to mix these smaller amount ingredients prior to adding to the batch. Make sure everything is mixed up real well which is a little easier when things are pigmented as these are.

I melt it at 2100 until pots about full. You can mix prior to cooking but I try not to. Chalcedony wants to go gray so don't do anything to push it that way! Cooking is performed with the following program:

2100 to 2180 and let soak for 10 hours.
Down to 1900 for 2 hours. (Fines the glass, removes bubbles)
Back to 2100 for work.

It may show no color upon gathering. Play with it. Let it cool, work it on the marver, heat it back up and let it go stone cold. Put heat back in and watch the colloids grow.

If you stretch it out you probably won't like it. A nice thick optic effect works well with this glass.

See Josh Simpson and Dino Rosen for the highest levels of implementation for these glasses.

*Black tin is a tricky ingredient. Pete swears you need 30g/10lbs, but this will turn black (actually dark amber) in my furnace. Try and it see what works best for you.