Thread: Phosphate Opal
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Old 04-11-2009, 07:52 PM
Dave Bross Dave Bross is offline
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Actual batch specs in a minute...

Now Pete, you know you raised me up better than to go around short on my modifiers.

I'm targeting 8% or greater total modifiers. That's correct about staying within the limits mentioned in the original post. Strontium or Barium are also modifiers and make up the difference to get up to the 8% total. I'm guessing you stock Barium. That could replace the Strontium. You're going to have to diddle your expansions anyway for your new Stevie Wonder.

I use Strontium to minimize toxicity. I figure it's setting things up for the future. One day soon the powers-that-be are going to raise hell and shut a lot of people down over the toxins in glass. Look at what they just did shutting down the jewelry in CA for lead and smaller motorcycles/4 wheelers (kid size) for tiny amounts of lead in places like valve stems and control levers????? Sheeeesh. Wait until they figure how much lead there is in import color. OK, enough soapbox oratory....now back to our regularly scheduled programming.

Here's what I've been melting in pounds:

Sand - 97.5
Soda Ash - 36
Hydrated Lime - 5.5
Strontium Carb. - 9
Zinc Oxide - 3
Borax 5 mol - 9
Alumina Hydrate - 4.5
Lithium Carb. - 1
Potassium Nitrate - 1
Sodium Tripolyphosphate - 6.5

In percentage:

SiO2 - 65.32
Na2O - 17.32
K2O - .32
LiO - .27
CaO - 2.82
SrO - 4.25
ZnO - 2.02
B2O3 - 2.95
Al2O3 - 2.18
P2O5 - 2.54

I did some melts that were 4% ZnO and 4.25% SrO with no calcium at all, other ingredients the same and they worked fine also. A little nicer working and a little brighter when clear before the strike or if not striking the glass all the way.

These formulas will pull from the pot clear and strike on cooling or when touched with something cold. Lot's of nice veiled effects possible with repeated gathers and strike control via temp.


This was designed to melt quickly at a low temp. (2100F)and it does that quite nicely. You could probably lose some/all of the Borax and recalculate if you wanted less Sodium, less furnace attack and higher melt temps. I haven't tried it. I suspect that with the modifiers adjusted to these lower specs that borax and lithium may not be quite as necessary for knocking down the Phosphorous as we all thought in the past. That's theory, I haven't tried it.

Even getting close to 18% alkalai there's enough Alumina to satisfy Nick Labino's old rule of total alkalai percentage divided by 8 being the minimum percent for Alumina. Some clear unstruck samples of these phosphates have been lying around outside in the Florida humidity for a while with no deterioration. Nick was the man...that rule works!

I was using a coffee grinder in early experiments with pelletized superphosphate fertilizer and they do indeed reduce things nicely.

Reading between the lines in that old patent, the Calcium and Zinc levels are the most critical thing.

If you wanted to use bone ash it just sneaks in under the allowed percentage of Calcium so your batch would want no other Calcium besides what's in the bone ash. This assumes you use the same percentage or less of phosphorous via the bone ash as up above. Thought I would mention that in case you've been eyeing grandma's ashes as a glass additive.

One more plug for Strontium. It's supposed to be the closest thing out there to lead in terms of appearance and behavior in glass...without the toxic downside. That was Mr. Volf's opinion anyway. There's some interesting info on this in "Chemical Approach to Glass" under the Strontium section. I think I should have a "stimulus" check from the Strontium producers by now, no?
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Last edited by Dave Bross; 04-12-2009 at 07:27 AM.
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