On our glass tempering furnace, we are seeing marks on the thick float we have never seen before. from 12mm to 19mm glass there is almost a pitting that occurs. the weird thing is that it looks like debris ot dust but there is nothing there to the touch. Its almost like the rollers themselves have imprinted the marks onto the glass. we have cleaned the rollers several times but this does not seem to help. the exit temp. of glass is 618-620 , so its not over heating. please assist where possible. I have never seen these marks in the 8 years that we have had this furnace, we use very little SO2 gas, in fact almost nothin at all. COULD IT BE THE ROLLERS???