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I'm wondering what might be causing a rough texture (looks like drag marks) on the underside of plate/tray brims after slumping??

After fusing my pieces have a nice, smooth, relatively shiney 'bottom'. Just a slight imprint of the wash and generally a nice finish I am happy with.

After slumping the back of the piece along the back of the brim of the tray or plate is an ugly, rough, matt finish that kind of looks like drag marks. Where the glass touches down and conforms to the bottom of the mold, however, this does not happen, here it is smooth and relatively shiney with a slight imprint of the wash and these areas look good. They are well slumped ( as opposed to slumped well).

Could this be caused from too fast of an ascent, or not holding at the top end long enough????

The molds are properly prepared SS, though they are not designed specifically for glass, and the wash is airbrushed and smooth.

Thanks so much for any feedback or suggestions.

janine

Janine (nice name - it's mine too!) it would help us to answer your questions if you told us the following:

size and thickness of your glass, size of your mold, and firing schedules.

My guess, without knowing any of the above is that you are ramping up too fast and slumping too high.

all my best,
Barbara

Hi Barbara

My sched. is 350 to 1000 - 0mins / 1200 t0 1230 - 32 mins/ 9999 to 1000 - 8min/ 300 to 955- 20 mins/ etc.

The molds are 9 x 9 square and 9 inch circle. It happens on both double and triple layers of Spectrum glass. It is worse on the square mold. It's kind of like the glass moves and then piles up before moving again, this is on the square mold. On the round mold (traditional plate shape) it looks more like it drags. The rim is about 1 inch wide and it affects the whole rim area.

I also have a 12 x 10 oval mold and on this one it occurs only slightly and only on the very edge of the rim. This has a more contoured shape and so the glass doesn't flow into all the contours, leaving a beautiful shiney surface.

Thanks very much. I thought your name was Barbara, Barbara?????

janine wrote:Thanks very much. I thought your name was Barbara, Barbara?????

Barbara Jeanine? One of my favorites!
http://www.absolutearts.com/portfolios/s/sherah/

Yep, Barbara Janine. My mother is Janine Noel (her bday is 12/25).

Janine, I think you are racing to the slump. Slow that 1200dph to 1230 down and you will probably eliminate your problem... I don't work with Spectrum, so am not familiar with the temps according to Spectrum, but I have found that it is just as effective with pieces that large to slump by going sloooowly between 1000 and 1150 and soaking at 1150 for 10-15 minutes. Of course if the mold is smaller or deeper, you will need to soak longer or go a little higher and then soak.

hope this helps!

Barbara Janine

Thank you Barbara Janine and everyone who responded off board. It seems that most of the problems encountered with glass can be solved by slowing down - in one way or another. This is probably true in life too.

Thanks again

Janine