View Full Version : coloring clear glass

Franklin Sankar
01-23-2017, 09:54 AM
Can you add chunks of rods to clear cullet and melt in a small color pot to make colors? Maybe as powdered color mixed with clear powder and mix into wet cullet.

Pete VanderLaan
01-23-2017, 10:04 AM
Well, you can. That doesn't mean it will look good or anything remotely like it. With many colors, it won't be recognizable. Rolling it in the powder or cullet is your only realistic option.

Franklin Sankar
01-23-2017, 02:00 PM
One color only per pot but I get your point

Eric Trulson
01-23-2017, 03:23 PM
I know it's been mentioned here a few times before, but saving your different color scrap (moils and any trashed pieces or cutoffs that have already had color applied) and melting it all together once you have a pot's worth tends to result in a nice light transparent blue.

Bit of a one trick pony (you're only ever going to get that one shade of blue, maybe a blue/green at most), and as Pete says, you're almost certainly better off saving any rod/frit/powder to use directly. It is a nice way to recycle glass scrap if you don't need perfect optical clarity though (I have yet to run one of those scrap melts without getting small bubbles and some cording).

Pete VanderLaan
01-23-2017, 04:31 PM
I don't know why it's always blue, but it always is.

Cecil McKenzie
01-23-2017, 06:23 PM
Cobalt takes one part in 5000 to make a visible color. If you never used any cobalt color it would not be blue.

Pete VanderLaan
01-23-2017, 07:34 PM
actually, one in ten thousand shows distinct color but it doesn't make it pretty. . Even so it always looks like faded blue jeans. Just ladle the heel.

rodman gilder miller
02-01-2017, 10:16 PM
The blues come through because the other colors are more radically concentration dependent: many of the yellows-orange-reds are a combo of selenium cadmium and sulfur. dilute it out a small amount and the color center doesn't form. Beer-bottle brown is sulfur and carbon combined . Copper and gold rubies have a colloidal color center with something like 1,000 to 5,000 atoms! We can expect that to be invisible with small dilutions. Cobalt and copper have colors which arise from a single atom in solution. They come through with a concentration dilution.

Dennis Hetland
02-10-2017, 02:12 PM
I use scrap sp cullet. I can't help, but put some pieces that contain some color in the pot. All colors "burn off". Greens and blacks become blue.
Yellows and reds disappear. Why? I believe it's because my furnace has an oxidizing atmosphere. That would mean(unless I'm wrong) that the holes in the atomic lattice are being filled, which prevents the larger, slower, yellow and red wavelengths from being able to pass while still allowing the shorter, more powerful blue wavelengths to pass.
Light is thought of as being both a wave and a particle at the same time. That's why a "wave "would need a space/hole in the valence belt.

Pete VanderLaan
02-10-2017, 04:29 PM
All colors "burn off". .
Actually, no they don't.

Dennis Hetland
02-14-2017, 05:07 PM
With the exception of blue that has been my experience.

Pete VanderLaan
02-14-2017, 06:40 PM
Don't confuse dilution with ionization. Many colors rely on specific balances to show their color. Cobalt is not one of those elements. Neither is iron and both can show a blue color. Copper can show blue as well. Cobalt just happpens to show color at one part in 10,000. Manganese can have its color dissipate in a reducing atmosphere but I would not refer to it as burn out but as a valence shift. Selenium can be in five states of valence. Only one shows color. Cadmium only shows color in the presence of sulfur. Cerium and Titanium can show a yellow but only when both are present and in the right ratio. Copper in reduction is a red sometimes, in oxidation, a blue, or a green, sometimes a gray. But it's not burning out.
It is the case that loss can be measured in micrograms per hour of lead leaving a melt based on melt temps. It goes up as the temp goes up. I am not convinced yet that selenium volatilizes in an existing glass but I do beleive it changes valence easily. Again, those type losses are in micrograms per hour. Selenium volatilizing largely is deemed to occur in the batch melt, not in a cullet. My best understanding is that sodium does volatilize as well to a lesser degree. Your color rods require a very fixed concentration to show their color. Chucking them in the clear is going to make the color dissipate in the goop.