Borax replacement in an unoxidised batch

[Mark Armstrong]

Since taking Pete's color class back in 2013 I have made a number of melts of silver opal glasses. I have always used Spruce Pine color base. For a variety of reasons I would like to start batching my own. Looking back through the archives, you mentioned Pete, that you were in a bit of an open revolt against Borax, seemingly for its aggressiveness to refractories and the dullness it bring to glasses. I understand that Spruce Pine is Borax free.
This silver opal will be gathered directly from the pot without being cased, so expansion is not an issue at this point.
Can I omit the Borax from my melt completely? Should I add a little Soda or potentially Potash to replace the Borax. Will additional Potash add to the brilliance of an opal glass.
Thanks in advance for any advice

[Pete VanderLaan]

Borax tends to make a melt get softer without changing the expansion much. It does scuz up recuperators and reacts with the refractories, particularly around the doghouse door. as a yellow stain, usually in the one O'clock position. it is really gummy and makes the door stick. In a moly it makes chimneys around the element bricks reducing the insulating efficiency of the furnace. So, of course it's in common use.

If you remove the borax, you might consider adding a bit of fluorspar if you have it and your furnace is not electric. Otherwise, I do love potash but soda ash may be more effective at keeping the melt easy even though it doesn't make color better. Lithium of course will really lower the melt conditions but these days, it's about 2,000 bucks a bag.

[Mark Armstrong]

Thanks Pete,
I'll put some numbers into the glass spreadsheet from class with Soda and Potash. I don't think I'll be springing for Lithium any time soon. Thanks.

[Pete VanderLaan]

If the furnace is electric, then the only way to really do it would be with either potassium or sodium nitrate, potassium being my preference.

[Mark Armstrong]

The furnace is gas. I am assuming I would want Soda Ash or Potassium Carbonate, as I do not want to use the nitrates in an unoxidized batch.

[Pete VanderLaan]

Well, I'd forgotten the unoxidized part of the deal. If that's the case, sodium sulfate would be one way to drive out gas as would the fluoride compound. Either way, it consumes time and that's the nuisance of unoxidized glasses.

[Mark Armstrong]

Thanks Pete,
Are those compounds intended to aid more in the melt of the glass and viscosity, or the fining of the glass, or both. I will look into both of those. Thanks

[Pete VanderLaan]

Reducing viscosity is part of fining. The other part is valence switch. The question is what happens to your color when you add different things. In General, I don't want sulfur in my melts and fluorine has turned silver batches grey.
You can just leave it alone and be patient which is what I normally would do.

[Mark Armstrong]

Thanks Pete,
So what I read from this is that I can delete the borax if I would like and adjust for expansion with Soda or Potash if need be. In doing this I would need to be a little more patient with the fining. Thanks for the input.

[Pete VanderLaan]

The other aspect of this is that the color base from Spruce Pine still contains lithium and will likely be subjected to some serious price changes. I have often wondered, but never acted on, the nitrates in silver nitrate and how they interact with the unoxidized stuff if you are melting silvers. If you are, I might suggest converting the silver nitrate to silver chloride. The process for that was in "Glassnotes" 3rd ed. I don't know what it would do, it's just a thought.

Also, for anyone considering the color base which was introduced by SP after Tom took my class, that it is not mixed at all. The chemicals to make it work are simply put in the bag one at a time. So, you have to mix the entire bag. I have always mixed my own unoxidized batch completely.

[Dave Bross]

Since we're talking batching from scratch, and softening/loosening up the glass, I might suggest replacing some or all of the lime with strontium.

Just be sure your alumina percentage is correct to avoid devit.

In case you're not familiar with this, add up any alkalies that are in the first column of the Periodic Table, then divide by 8. That's how much alumina you'll want in there.

One other thought....borax is just about "self-cancelling" in terms of how much it moves the expansion, which is something in the neighborhood of a few tenths of a point, so putting it in or leaving it out will be very close to the same expansion either way.

[Pete VanderLaan]

He's using SP color base with his own a possibility.

My experience tells me that when you add more than two things to a glass at once, you rarely learn anything except to not do that. .

[Mark Armstrong]

Thanks Dave and Pete,
I do recall the mention of the Strontium. I will look into that when I can get into the pottery supply.
I also have some silver chloride laying around so that is something for the future also. Thanks for all the help and suggestions.
One thing at a time, as time permits

[Pete VanderLaan]

Strontium has its greatest value in phosphate opal glasses where you are trying to avoid making big awful calcium phosphate crystals. It does that job extremely well but it is still something of an expense. Calcium carb is quite adequate for simpler applications and costs tons less. Dave's Brossphate opal does a very nice job with the strontium. Mark has always used it as well. I use what seems necessary. Think zinc and barium as well.