I fired a piece with buf 1116,buf0420,buf0014,buf1821,buf0243,wis90-12 .
clear 1100 was covering on them.
First I used new shelf , a piece was successful. But second time, the pink stain and black stain appeared .
The pink stain spread on the side of the shelf.So I could get rid of it by sandblasting.
But the black stain sread between those colorful glasses and clear 1100.That's why I couldn't scrap off.
I thing the pink stain is caused by reaction from previous fired glass color.
I am going to create 40 plates . I searched the solution of this problem in this forum. Then I knew that before the next firing, the shelf should be fired for cleaning the coppar and lead.
I wonder how degreee of kiln temperature should I raise? and how many times should it be fired ?
I don't understand the cause of black stain. I attept the pictures. Please give me solutions.