Hot Spots during Fire Polishing
Posted: Tue Feb 25, 2014 4:03 pm
I'm having trouble with what I call "hot spots" on some of my pieces during fire polishing. Here is what I'm doing:
I construct, full fuse a piece, anneal well, etc
I will then cold work the edges and the new top if I do a flip & fire so I have a smooth surface. I will use the pneumatic angle grinder to level out any deep or high spots and then I hand lap with 220 silicon carbide grit. I will usually sand blast one last time to make sure all surfaces are evenly covered.
I then slump and fire polish, here is my schedule:
300/1000/10
600/1235/10
AFAP/900/ hold depending on thickness
the rest of the schedule is depending on thickness again--I use the BE chart
Some pieces come out with an awesome matt finish and slumped nicely in the mold (plate molds or shallow platters, nothing deep).
Others come out with 97% awesome matt finish, but with spots of gloss here and there. Its quite annoying. I will re-sandblast and fire polish again (at a lower temp), it would work, but then a new piece will have hot spots at that lower temp, while others won't. How can I get a consistent look across firings?
Do I either lower the temp and hold the time more
keep the temp, shorten the time
or both?
For other reference:
the hot spots are not closer to the side elements
I've moved the mold around the kiln looking for a better spot--no joy.
Any help you can give, would be helpful.
(in the image attached, there was as 'hot spot' was to the upper left corner of the red window, everything was great. very frustrating. Also, not the best picture--iphone and all. )
I construct, full fuse a piece, anneal well, etc
I will then cold work the edges and the new top if I do a flip & fire so I have a smooth surface. I will use the pneumatic angle grinder to level out any deep or high spots and then I hand lap with 220 silicon carbide grit. I will usually sand blast one last time to make sure all surfaces are evenly covered.
I then slump and fire polish, here is my schedule:
300/1000/10
600/1235/10
AFAP/900/ hold depending on thickness
the rest of the schedule is depending on thickness again--I use the BE chart
Some pieces come out with an awesome matt finish and slumped nicely in the mold (plate molds or shallow platters, nothing deep).
Others come out with 97% awesome matt finish, but with spots of gloss here and there. Its quite annoying. I will re-sandblast and fire polish again (at a lower temp), it would work, but then a new piece will have hot spots at that lower temp, while others won't. How can I get a consistent look across firings?
Do I either lower the temp and hold the time more
keep the temp, shorten the time
or both?
For other reference:
the hot spots are not closer to the side elements
I've moved the mold around the kiln looking for a better spot--no joy.
Any help you can give, would be helpful.
(in the image attached, there was as 'hot spot' was to the upper left corner of the red window, everything was great. very frustrating. Also, not the best picture--iphone and all. )