contact marks when slumping

Cristi · Post by **Cristi** » Wed Apr 07, 2004 2:06 pm

hello all-

the question is...why do my pieces end up with shiny contact marks from the mold? am I overslumping? it seem that i either have a well defined shape with glossy spots at corners etc, or a well intentioned not quite "there" piece . I actually like the matte underside and the shiney bits look rather unfinished.

any sugestions?

many thanks,
cristi

charlie · Post by **charlie** » Wed Apr 07, 2004 2:17 pm

the shiny places are because that part of the glass didn't contact the mold. the dull places are where it touched the mold.

you might try sandblasting the back evenly before slumping. a 5-10 minute soak at 1225 will give it an all over matte finish.

Cristi · Post by **Cristi** » Wed Apr 07, 2004 3:52 pm

I think the shine is from contact,not lack of contact...the pieces are matte to begin with. Cristi

Cynthia · Post by **Cynthia** » Wed Apr 07, 2004 6:41 pm

If I understand your question...the phenomenon is caused by the glass stretching. The shine is where the glass is pulling in order to bend or stretch downward into your mold. Where the glass stretches the most it will become the most shiny...where it comes in contact with the mold it will pick up the texture of the mold. I think Charlie is right that this shiny underpart isn't touching your mold...but take this info and sort out what you see with what you know and I expect you'll figure it out.

Try bending at a rate of 100 dph (starting from 1000F) to 1150 or 1200 (When it's fully slumped will depend on the mass and span of the glass and the slope of the mold) and add a hold only if necessary. The cooler temps and slower rate will cause the glass to bend more evenly and slowly so you will see better results overall...but it still may not eliminate the shininess you refer to.

Stephie · Post by **Stephie** » Thu Apr 08, 2004 2:02 pm

Charlie, the soak you refer to is on the slump fire?
Do you do this on the ramp up or on the ramp down?
Are you both saying that you slump at ~1225? Are you using bullseye?
Thanks, Stephie

charlie · Post by **charlie** » Thu Apr 08, 2004 2:10 pm

Stephie wrote:Charlie, the soak you refer to is on the slump fire?
Do you do this on the ramp up or on the ramp down?
Are you both saying that you slump at ~1225? Are you using bullseye?
Thanks, Stephie

the schedule i use for slumping largish bowls that i want a matte finish on both front and back is:

250 1125 0
50 1175 0
9999 1225 10
9999 970 30
anneal

depending upon the size (span), it's usually slumped long before it hits 1175. the wider the span, the quicker it will slump. i can then do a quick reprogram, or just wait it out until it gets to 1175.

i use only b.e. although i just got a 4'x6' sheet of 1/2" float to play with.