Torch working batch glasses

[Rich Federici]

Sometime ago I remember Dave Bross having formulated a glass for pulling down as rod to be flameworked.

I have looked at some of those posts, and in addition have found that SP87 that we pull down for clear lampwork rods behaves quite differently compared to Morretti.

Two things that appear are the flare from the glass with spruce pine turns a shade of magenta, as opposed to just yellow with morretti. Also, the surface of the Spruce Pine tends to foam up more easily than the Moretti.

Any thoughts as to what ingredients in one vs the other should be either added or left out of a homemade batch glass which cause these characteristics to occur?

Thanks,

[Ray Laubs]

Ive heard good things about Gaffers batch in a torch situation.
Currently Im using sp87 and it handles a lot better with a surface mix torch instead of a premix.

[Drew Fritts]

Rich,
I can't tell you what to add or leave out, but unless you're mixing your own for the thrill of figuring it out, get some Gaffer batch and pull it into lampworking rods. It's the best batch I've found in the 95-96 LEC range for lampwork. Most of their colors work well in the flame as well, but then, so do a lot of R and K colors.

Drew <+><

[Franklin Sankar]

Rich can you explain some more about the problem? Like is the effect of the foam? what does the flare cause etc
If I hit my home brew cane too quickly with the torch it shatters. I have to heat it up a long time .
Does the same thing happen to your SP? what about Gaffer.
Thanks
Franklin

So much still to learn.

[Rich Federici]

So, I have this formula for a base clear, of an LEC of 96, and I have an LEC 104 formula. Here's what's in each:

LEC96 Clear:
in Pounds,
63.25 Silica
20.25 Soda Ash
9.06 Hydrated Lime Type N
2.18 Borax, 5 mol
5.25 Potassium Carb.
100 grams, Antimony Oxide
130 grams, Potassium Nitrate

This makes a great Clear, but using rods from it in the torch, the surface foams easily, and we notice a magenta flare from the glass. The flare is no big deal in itself, but maybe someone may know what this may be an indication of.

Now, the 104 formula:
I have not melted this yet, but understand from the archives that it fits Moretti well. We notice when we work Moretti in the flame that a yellow flare comes from the glass, and that the surface does not bubble like the other (96LEC) formula does.

85.5 Silica
27 Soda Ash
12 Potassium Carb.
1 Lithium Carb
8 Hydrated Lime
5 Strontium Carbonate
3 Borax 5 mol
3 Alumina Hydrate
.44 potassium Nitrate (200grams)
.22 Antimony oxide (100 grams)

So, I'm seeing Strontium, Lithium, and Alumina Hydrate in the 104 formula, and I guess I am asking if any or all of these different ingredients are what may have an effect on how the 104 will behave in the torch.

And... can I add them to my 96 formula to make it more workable in the flame?

I don't think I want to melt the Gaffer formula, nothing against it, but I have come this far and need to understand this a little better to get it right, and then I can go from there.

Thanks for your help.

[Dave Bross]

Rich,

Let me see if I can help here.

I had the foaming problem with SP and my own batch in the beginning. Cutting the Lithium below 0.2 percent was the only way I could get it to stop on my mix.

Lithium

I was assuming the high Lithium percentage in the SP was why it wouldn't torch well, but that's not scientific documentation by any stretch. Could be one of those "numerous coincidences do not equal data kind of situations. I did do a lot of melts and the problem stopped every time I cut the Lithium below 0.2 percent.
My best description of Lithium is that it makes glass melt FAST and at lower temps., and really speeds up the reheats. It's an alkaline flux like soda or potassium but way more powerful. Higher percentages are rough on pots too.I think the high percentage in SP works because the lithium is in there as a spar, combined with alumina, so not as prone to go after the pot walls. Just a theory. Expensive

Strontium

It's a modifier, similar effect as Lead or Barium, but not extremely toxic like those two. Brightens up the glass, makes a faster melt with less seeds than lime, makes it long and buttery to work, helps with devit resistance. More expensive than lime but makes much prettier, better working glass.


Alumina

Used primarily to prevent devit. It shortens working time and stiffens the glass. You almost can't blow glass (unless you counter with Lithium or other flux) of over 2 percent alumina. You would classify alumina as a glass former, like sand. It raises the melting temps. of the glass a lot.

Those old formulas I posted will work in the torch, but if I had it to do again today I would try some changes. Volf wrote a book on technical glasses that went into this problem. He discovered that the problem was boiling the alkalai off the surface of the glass without enough coming up to the surface from below to replace it. When they finally got the ability to analyze the lampworking glasses that were known to work well they found the common denominator was 3-4% of alumina and over 15 percent alkalai. Borax was also found to be very helpful. The alumina slowed down the boiling off.

If I had to make a glass just for lampworking I would begin by upping the alumina to that 3-4 percent, or more, and have some borax in there and no or low percentage lithium. We definitely clear the 15 percent alkalai at 96 coe. It would be just a lampworking glass too, because it wouldn't blow due to stiffness. Later on I would try and put the Lithium back, going higher on alumina to see if it countered the boiling.

If you want more info from that book I'll dig it out for you.

Oh yeah, one other warning, that first formula is the one Pete gave me modified a bit for coe. It's a beautiful glass but it will devit if it's anyplace very moist, like here in Florida.

I have no clue what the magenta flare might be.

Gaffer clear batch is truly excellent lampworking glass, with one warning...if it gets reduced much it will turn grey. Their website mentions that they replaced a lot of the alumina with zinc, so that might be what greys. I'm not convinced of that because I use zinc in my clear and haven't turned it grey yet, and my glory is a venturi, so somewhat reducing by nature. The zinc makes it melt and work better.

[Rich Federici]

Dear Dave,

That's exactly what I needed to know.

We wouldlike to try a 104 melt for my wife to have as lampwork rods.

I am thinking that I can make a clear that we can lampwork that will not have the bubbles and stuff that we find in moretti clear rods on occasion.

Your response gives me the information that I need to go ahead and work on something for our situation.

Thanks again!

[Jon Myers]

I've seen some nice lampworked spectrum nuggets as well.

[Dave Bross]

I'll throw in a few" tricks" too.

Put about 0.5 percent of phosphorous in there and it will clean up some of the green and make the glass way brighter. My favorite source is sodium tripolyphosphate but at that small percentage any of the easy to find calcium phosphates like bone ash will work just fine. The calcium phosphate works in pre mix batch too because the small amounts don't throw the coe too much.

One or two percent zinc helps the sparkle quite a bit too. Not to mention better melting and workability. I cut the lime back in the same percentage I add zinc, or at least make sure I have 8 percent total modifiers. Let me know if you get grey under heavy reduction?

I make clear batch without potassium using soda as the primary alkalai. Use the phosphorus and zinc and it is just as pretty as a glass with potassium. It doesn't polish as well as the glass with potassium but few people would notice unless they compared the two side by side. I save potassium for the colors that really need it.

Here's a handy list from Mr. Volfs book on accepted ranges of material for lampworking glasses in percentage:

SiO2 - 60-70
Al2O3 - 1.5-5
B2O3 - 0-3
CaO - 4-8
MgO - 0-4
BaO - 0-5
ZnO - 0-7
Na2O - 12-22
K2O - 3-7

Don't use any more of any flux than you need to get the effect. The prettiest lampwork glass is the one with the most sand and alumina in it.

I use borax to drop the viscosity at working temp and to increase working time too. If you're encasing things in clear with a torch viscosity becomes an issue and more working time doesn't hurt either. Borax seems to harden the glass so requires more polishing time if you're cold working. More speculation on my part there.

Way better to use the hot glass right out of the furnace to encase when possible.

You're going to enjoy this. Moretti clear is a terrible quality glass.

[Dave Bross]

I've been forgetting to answer Franklins question.

You need to preheat the cane, and if it still shatters then you pulled it too long with the glass too cold.

I preheat cane in the torch by passing it through the flame rapidly in an up and down motion, about one second each way.

[John Cramer]

Originally posted by Dave Bross
I've been forgetting to answer Franklins question.

You need to preheat the cane, and if it still shatters then you pulled it too long with the glass too cold.

I preheat cane in the torch by passing it through the flame rapidly in an up and down motion, about one second each way.

Here's another technique that works when dealing with shocky glass. Turn the oxy off at the torch and preheat the cane in a pure fuel flame. The lower flame temp will preheat fairly quickly without any breakage. Once the glass is preheated kick the oxy back on, it'll burn off the soot and you're good to go.