----------------------------------- Mircea Pteancu 28 Aug 2008 18:27 ----------------------------------- Si iata si vestea buna pe care o puteti citi mai jos.Procesul de ''slumping'' nu dureaza asa de mult cum ne-am temut,in nici un caz nu de ordinul saptamanilor sau lunilor .In postul de mai jos ,de pe ATM Email List, e vorba de un program de o zi si jumatate.Procesul de ''slumping'' presupune existenta unui cuptor cu temperatura controlata (cel de mai jos cumparat la ''second hand'' cu 25 parai),a unui disc de sticla si a unui sablon de forma concava al carui negativ devine discul de sticla.Acesta devine deci un menisc avand curbura aproximativ egala cu cea a viitoarei oglinzi.Economie de manopera si abrazivi cat si faptul ca forma de menisc este mult mai stabila mecanic decat discul clasic:forma da rezistenta si rigiditate cojii de ou.Dupa ce a invatat prin tatonari cum sa stapaneasca procesul de ''slumping'',raportand vreo zece esecuri pana acuma,David Davis vrea sa-si faca mult visata oglinda de 36 inch adica 90 cm diametru.Mircea ........................................................................................................... When the glass folks talk about working warm glass what they want is a fast job. They ramp up the heat as fast as they can to specific temperatures, hold the glass there and then run it down. The problem is my old kiln that I bought for $25 will not ramp up fast. Nor does it have the construction to efficiently manage heat. What broke the other two large blanks, and several smaller blanks was trying to run my old kiln like one of the new high efficiency models. I had to learn that. I had to learn how to run my kiln. I finally figured out that goal of the melt was to take the glass to slumping temp, then drop it quick before it slumps too much, then hold it at anneal, then strain, then cool. IT doesn't matter how you get there, you just have to hit those points. My program to slump the mirror blank was .. ramp up at 100 degrees an hour to 1200 degrees Hold for 20 minutes Fall to 900 Hold for 5 hours ramp down at 100 degrees an hour to 800 Hold for 90 minutes ramp down at 100 degrees and hour to room temperature That ramping speed is so slow that it is very gentle to the glass and heats it more uniformly. Because of that I can slump at 1200 which I think is easier on the glass. It took a day and a half to run the program. I made the mold by tamping sand into the bottom of the kiln and shaping it with a curved piece of wood and a paint brush. The weight of the glass collapsed the mold and I did not get as much curve as I needed. I reset the mold using a ring of plumbers tape for the edge of the glass to sit on and refired the glass. The glass looks good, the curve looks good. Next project is the 36 inch thin blank. David Davis Toledo, OR 97391