scrap cullet colouring

[Mark Armstrong]

So I have a question regarding what might be happening with some recylced cullet a friend has been trying to colour. As a cullet he is using pipe crack off and broken cullet from broken pieces, all spectrum nuggets, all with an assortment of colour bar colours attached. A real dogs breakfast. First attempt at purple using 275 lbs of cullet, added to this was 2.5lbs of manganese dioxide and 2.5lbs of something called "no salt". From what I could find this is approx 51% potassium and 47% chloride. This produced a pale grey, that became more purple towards the bottom of the pot. This seemed to make sense to me.
The second attempt was the 275lbs of cullet and 2.5lbs of manganese dioxide, but NO "no salt". The result was a very lumpy darker green with what looked like small black stones.
Supposedly the batch and melt procedures for both were the same. Done in a Nat gas fired furnace. Does the potassium have that great of an effect. I know all the bits and pieces of colour can effect things, but to this extent?
Just curious, not something I would attempt

[Pete VanderLaan]

It sounds like an ice melt.
From my point of view there are too many variables to draw any conclusions at all. Color rod /crack offs are not something I would consider melting Mark. Most have lead in them, just so many differing formulations. Then there's the iron shed from the pipes. When Manganese gets around any reduction it will dissipate. Is there perchance a reducing atmosphere in the furnace.

The stones have the sound of Corrundum from chrome. That's consistent with the green tone. Potassium does have a substantial effect on shifts in color.

[Mark Armstrong]

Thank Pete,
That's exactly what I was thinking. Merry Christmas ,
Happy New Year.

[Pete VanderLaan]

As to the blue. It is said that one part cobalt in ten thousand shows distinct color. Given that concentration and then wondering about the cullet being used to try to make the gray, it seems to me that you are shooting at a moving target. How many extra chunks of cobalt do you suppose it might take to change the color from one shade to the next? So, that's problematic. Anytime I have used cullet to make up a color which is really rare, I do not use anything but clear. The cullet that has been mentioned is a real witches brew of differing basic formulas. Differences from melt to melt would be what I would expect.

Iron can make blue too. washed out, but blue. It always come out blue.