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Dave Bross 04-11-2009 08:52 PM

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 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?

Pete VanderLaan 04-12-2009 08:36 AM

What form were you introducing the strontium in? And... what did it cost in bag quantities? Are there 50lb bags of strontium (Carb, 90 , ) what? Can we make glowbars from it?

And did you ever get a L.E.C. on the stuff. I willl target it to a 96. I don't think I have strontium in the spreadsheet.

And with 150lbs of the tripolyphosphates coming this week and our soil not needing phosphates at all, I'm committed to the polyphosphates for a while at least. I have plenty of barium. And I have got to get my copy of Volf back from Mark Peiser.

Dave Bross 04-12-2009 10:18 PM

Strontium Carbonate, $1.75 a pound in a 50# bag. If all else fails all pottery supplies will have it. This isn't going to help in New England but I got it from Davens Pottery Supply in Atlanta for less than what the major chemical supplier wanted.

About the glowbars, this stuff is no relation to the radioactive Strontium 90 and not useable as a silicon carbide heating element so I think that covers both possible answers there?

In my E&T spreadsheet I'm using a factor of 1.38 for Strontium to calculate expansion. I had forgotten that it's nearly identical expansion to Barium at 1.40 so there's an easy substitution.
That batch I wrote out will come in at 96 in my tiny melter but will probably be off a good bit in a melter with power.

Here's some from Volf from the Strontium chapter:

"Because of its identical charge and similar effective radius, r1, Sr is sometimes compared with Pb, despite the differing electron configurations of the two elements. The latter are reflected in the different polarizabilities of the two elements and their properties in glass. Pb as an ion of a B-subgroup element with a high atomic weight is twice as polarizable as Sr. In contrast to Pb, Sr with its lower atomic refractivity neither decreases the surface tension nor concentrates in the glass surface. Electrostatic charges therefore are not created on the surface of Sr glass by friction, as is the case with lead glasses. The closeness of the radii of Sr and Pb is responsible for the possibility of replacing considerable amounts of lead oxide in glasses containing 30% of PbO; in this way, Partridge reduced the PbO content from 30 to 20% by introducing 2-15% wt.-% of SrO."

There's more about how Strontium fines/melts better because it fluxes at a lower temp. and puts less gas into the melt than Barium.

Reading between the lines elsewhere in that chapter, Strontium does somethiing odd at over 15%, no particular details there as to what.

Another important point from Volf, Strontium glasses must have alumina in them or they will be less water resistant than calcium glasses.

Pete VanderLaan 04-13-2009 06:19 AM

Thanks, that will save me a bunch of time finding the playing field. I was joking about the strontium 90 stuff. That is really interesting. I called Peiser last night and told him he has to copy Volf and send it back to me.

Dave Bross 04-13-2009 08:44 AM

My pleasure.

One other "playing field" observation. Phosphates will be a slightly different E&T number than the usual number that works for a particular furnace for other glasses. Not so far off it wouldn't fit, given fairly liberal guidelines for a match...or at least it's that way it is here, which, of course, may not be an issue in someone elses equipment/location.

Rollin has been melting these for a little while so he may have some observations too.

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