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Sean Jones 04-29-2020 01:08 AM

Beginners using colour
Iím a self taught beginner working in the garage at home.
In lockdown líve finally allowed myself to use the colour bars I bought on eBay ages ago. Till now Iíve just used clear and found judging the heat in the gloryhole really challenging, along with everything else. A bit of transparent colour though makes the temperature much more visible. I can see whatís happening as I build up heat!
So, should I add a small amount of cobalt to the pot each time? A pale blue would be nice. If so how much cobalt carbonate per kg? Iím melting crystalica.

As an aside, I just bought the ďglass blowers guideĒ videos and at my level they are great. As are Boyd Sugikiís videos on the Corning web site. There is so much to learn and plenty of room for more tutorials on line if anyone is up for it.

Josh Bernbaum 04-29-2020 06:12 AM

I agree, I'm almost always using colour in my work so that when I occasionally make an all clear piece, I have a bit of trouble judging the heat sometimes. Sometimes.. You won't need much cobalt, since it's such a strong additive. You will need a decent gram scale (down to tenths or even hundredths of a gram) if you want repeatable results. One gram of cobalt oxide in 5 kilos may even be more than you want, which may be slightly different with the carbonate. You can do small test melts, see if you like the tone, and then multiply for larger melts. Take good notes for later.

Pete VanderLaan 04-29-2020 08:35 AM

1 part cobalt in 10,000 shows distinct color. It's the mixing it in evenly that's hard. In batch, it's not quite as hard. You can make powder blue which takes one part cobalt and mix it with one hundred parts batch. Then take one part of that and mix it with one hundred parts batch. That mix will allow you to measure out reasonably repeatable portions. If you don't do it in batch, use finely fritted or crushed cullet. It still needs to be mixed, or if not mixed, then pressure air mixed as melted in the pot which is a risky thing to do.

Gram scales are really helpful as Josh notes.

Cobalt carbonate is an easier way to put the cobalt in since gram for gram, there's not as much cobalt.

Art Freas 05-04-2020 08:52 AM

For Pete here, if you mixed the cobalt in with a lot more clear powder glass of the same COE, like 2 grams to 10 pounds and then physically mixed it, could you use that a an add to the powdered batch and then mix that? Would that make adding just a bit easier?

Pete VanderLaan 05-04-2020 11:32 AM

getting it even is a preposterous endeavor with cullet. It is just not going to happen with grains the size of an ant next to a chunk the size of a golf ball. Indeed it will turn streaky blue but batch additives are the way to go. Try making a fluorine opal in cullet.

As long as the glass community turns away from the pursuit of quality through persistent applications, it will get what it gets. I used to not understand how coloring glass would vanish as applied information every other generation but it's easy to see why now.

A demo for GAS back in St Petersburg was done on adding color to cullet, much of the information coming out of the archives here. I have a friend who was at one time the president of GAS who wrote to me wondering how the presentation ever got out of the selection committee. When I consider all of the work that has been done by real shining lights in the field, it's hard to believe it happens. I think of Chuck Savoie, Mark Peiser, Dick Ritter, David Hopper, Fritz Dreisbach, Jim Lundberg, Steve Correia and many more I apologize for not mentioning. They sought the very best. Those pioneers of the latest round of forgotten methods are the ones I turn to. Knowing that Mark went to Weyl's door and asked questions is something I would have died for.

Josh Bernbaum 05-07-2020 08:13 AM


Originally Posted by Pete VanderLaan (Post 147696)
You can make powder blue which takes one part cobalt and mix it with one hundred parts batch. Then take one part of that and mix it with one hundred parts batch.

Pete, I'd like to try a lightly-colored cobalt phosphate soon when I get my color pot back up shortly. Do you think I could make a 'powder blue' just with silica? My thinking is that instead of mixing it in a full-batch base, I could keep the extra mix around and have more versatility into what batches I can later add it to. And then just add some of this mix as a substitute for some of the sand in whatever formula I want colored a light blue?

Pete VanderLaan 05-07-2020 11:53 AM

That should work quite well. Keep in mind that silica really lowers expansion more than most folks realize. It's my go-to element when I was the expansion down. Substituting that form of powder blue for silica should be easy.

Josh Bernbaum 05-07-2020 06:28 PM

Cool, thanks for that.

Hugh Jenkins 05-10-2020 09:40 PM

Keeping track of zeros is really important in calculating color, and especially with cobalt. Diluting with silica to make powder blue makes slight errors less impactful, but parts per hundred or thousand or ten thousand are way different so do the math well. A mistake of grams of cobalt oxide in any formula is astounding.

I totally concur with the heat judgement with slight color in the glass. I always started the beginners with remelted scrap. There would be enough color from the pipe slag and color being used in the lab without any additions. The color would be slightly different every day, but copper, chrome and cobalt generally set the tone. One bonus of slight tramp color is that reactions with silver or other oxides is emphasized.

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