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Overfire Black Magic?
Posted: Fri Apr 11, 2003 8:05 am
by Paul Tarlow
Does Black Magic react with glass if over fired (1450F x 10min). I've got a bunch of gray/black glass in my kiln that wasn't that color when I put it in.
- Paul
Posted: Fri Apr 11, 2003 8:42 am
by Ron Coleman
Black Magic (Back Magic) has a high lead content and wil turn dark in a reducing atmosphere in the lkiln. I don't know if the process is reversible if you fire again with the vents open.
Ron
Posted: Fri Apr 11, 2003 3:23 pm
by Paul Tarlow
Ron Coleman wrote:Black Magic (Back Magic) has a high lead content and wil turn dark in a reducing atmosphere in the lkiln. I don't know if the process is reversible if you fire again with the vents open.
Ron
Doesn't there need to be something in the kiln to make it a reducing atmosphere? Also, it seems that only certain colors turned dark (black).
Curious if anyone else has seen this -- and if it ever happens at lower (1000F) temps.
Posted: Fri Apr 11, 2003 7:06 pm
by Ron Coleman
If only certain colors turned dark then there is a reaction between the glass color and the Back Magic. I know if you put any lead bearing overspray on BE French Vanilla it will turn dark.
Ron
Posted: Fri Apr 11, 2003 7:07 pm
by Cynthia
It's probably a reaction between the glass and the Back Magic. The lead in the Back Magic reacts with glasses that have carbon in them. I am relying on memory, so carbon might not be it....such as BE's French Vanilla. It's the same reaction you might see with a turquoise glass (reactive element is copper) next to a yellow glass (cad / sel). Brown to black discoloration...in your case splotches.
This is what I learned in a glass fusing class, but since it is ancient history...I may have inadverantly revised it
...Don't take my word, do the research to see if I have it right...If I remember correctly, these are the reactive elements and they don't play well with others. Lead reacts with carbon and CSS (cadmium /selinium?), copper reacts with CSS (cad/sel?) and carbon.
What glasses are these? I'd have to look at my chart to see.
Sray A will do the same because it contains lead, which is why I use either SuperSpray or Borax.
You might be able to blast or grind it off, but don't really know how deep the stain will penetrate.
Posted: Sat Apr 12, 2003 12:19 pm
by Lani McGregor
I agree with Cynthia (mostly)
Lead (and Back Magic has lots) will react with sulfur to make lead sulfide (black/brown). Many amber colored glasses contain sulfur (called “carbon/sulfur ambersâ€
Posted: Sat Apr 12, 2003 12:51 pm
by Cynthia
[quote="Lani McGregor"]I agree with Cynthia (mostly)
Lead (and Back Magic has lots) will react with sulfur to make lead sulfide (black/brown). Many amber colored glasses contain sulfur (called “carbon/sulfur ambersâ€
Posted: Sat Apr 12, 2003 6:30 pm
by Paul Tarlow
[quote="Lani McGregor"]I agree with Cynthia (mostly)
Lead (and Back Magic has lots) will react with sulfur to make lead sulfide (black/brown). Many amber colored glasses contain sulfur (called “carbon/sulfur ambersâ€
Posted: Sat Apr 12, 2003 11:10 pm
by Bert Weiss
Lani McGregor wrote:I agree with Cynthia (mostly)
Lead (and Back Magic has lots) will react with sulfur to make lead sulfide (black/brown). Many amber colored glasses contain sulfur (called ?carbon/sulfur ambers?).
Lead will also react with selenium to make lead selenide (black/brown). Many red and orange glasses contain selenium (Cadmium / Sulfur / Seleniums or CdSSe)
If the Back Magic is turning something other than an amber, red or orange glass dark, I'd be interested to know what the glass is.
L
Lani
Gee did you ever imagine that you would become a leading expert in glass chemical reactions
My grades in HS chemistry were C,B,A,A,A,D
