compression mark in small handkerchief bowl

[seachange]

Hi, wondering if you could please help me with this problem.

I am making tea lights for a gift shop.

Handkerchief vase type, prefused square blank, single layer tekta with some colored frit balls as decoration.

Slumping over round ceramic kiln props, 3" tall. This gives me the shape I was after. The square corners of the blank drop almost vertical, leaving just a sufficient opening to insert and remove the tea light. Have tried the floral formers, those give a more open shape.

But, with this deep drop of the corners, I get compression marks inside the outer folds.

So, when I look at the finished tea light, I have the shiny pointy corners nicely shaped, alternating with the hazy looking outside folds.

Here are the details:

Kiln: Evenheat, large coffin model (making several tea lights in each firing)

Program in centigrades
222 - 677 - 30'
333 - 804 - done
then the anneal

In farenheit:
400 - 1250 - 30'
630 - 1480 - done

Hoping for your help, have committed to deliver end of next week...shouldn't have .
Many thanks, seachange

[Stephen Richard]

I never take my hankerchief drops beyond 700C

[seachange]

I never take my hankerchief drops beyond 700C

Hi Stephen

Would you mind sending me a PM with the ramp ups and holds you use to get to 700?
Your firing must be much slower and longer than I am using.

I usually do a lot of tests, but I am in a bit of bind with the delivery time.

Would love to get this right.
Many thanks, seachange
PS: have been reading your blog lately, lots of very good, accessible information there

[seachange]

So very sorry, wrong slumping schedule, my apologies.

Here is the right one:

Centigrades

150 - 600 - 15'
afap - 620 - 15'
afap - 640 - 15'
afap - 660 - 15'
slump was ready at 660 with 5' hold

The kiln took 2 minutes from 600 to 620, 14' from 620 to 640, 10' from 640 to 660.
If I slow down instead of all the afaps, will it work better??

Farenheit
270 - 1112 - 15'
afap - 1148 - 15'
afap - 1184 - 15
afap - 1220 - 15'
ready at 1220 with 5' hold

Many thanks, seachange

[Stephen Richard]

I will be going into the studio later today and will get the schedule for you.
The answer to your question is "yes, slowing down will help."

[seachange]

I couldn't finish the blanks planned to be fired today, so decided to run another test.

Have changed all the afaps to 40C per hour, this is adding 30' to each section. Kiln is now at 630, I am peeping often through the view hole, corners haven't quite fully slumped yet.

Will have to wait till tomorrow morning to see if I am still having compression marks...I am going to get up extra early

Will let you know what happened. Would much appreciate to have your schedule when you have the time, just in case mine is not quite right yet.

Many thanks, seachange

[Stephen Richard]

My schedule was approximately (I forgot to look up the schedule when I was in the studio)
150c/hr- 650C, 20 mins (observe)
skip to 515C, 45 mins (tack fused pieces)
80c/hr - 370,0
off

The observation is essential for me, as different arrangements of pieces used

[seachange]

My schedule was approximately (I forgot to look up the schedule when I was in the studio)
150c/hr- 650C, 20 mins (observe)
skip to 515C, 45 mins (tack fused pieces)
80c/hr - 370,0
off

The observation is essential for me, as different arrangements of pieces used

Hi Stephen

well, no luck. The slump finished at 640C with a 5' hold, but the compression marks are still there. Perhaps a fraction less hazy, but still very different from the glossy corners.

Will try today on a floral former. This shape is more open, this might not create the problem at all.

Not exactly what I wanted, but ....

Many thanks for all your help, very much appreciated....still reading through your blog

Best regards, seachange

[Stephen Richard]

OK. Try a circle of fibre board a little larger than the kiln post. This may keep the glass away from the side of the post. You probably will have to dig out the fibre board though.

[Laurie Spray]

fiber board with a circle of thin fire.......turn to dust...no digging

[Stephen Richard]

Laurie,
I don't know what ceramic fibre board you use, but mine holds together. It is not hard, but certainly firm. Even my 3mm ceramic fibre paper does not turn to dust.

[Faye Malench]

Seachange, try a test run with regular or crystal clear. It could be the Tekta causing the haze you are seeing.

[Valerie Adams]

A photo would be really helpful!

You may not be seeing 'haze' at all; in asking glass to bend at extreme angles you'll often see 'stretch marks'. It's really hard to know what you're seeing because we may all be using different terms...

[seachange]

Seachange, try a test run with regular or crystal clear. It could be the Tekta causing the haze you are seeing.

Hi Fay

many thanks for replying. The "haze" are compression marks, because of the extreme bending angle. I thought this could be avoid by slowing the firing further. It reduces the haze slightly, but it is still there.

All other areas except for these extreme folds are completely clear. Haven't been having any problems with the tekta, I am fusing the blanks on kiln washed shelves (no thin fire), it comes out totally clear.

Have decided to show them to the gallery as they are, and see if they consider this a natural part of the process, if one wants to achieve this very narrow shape. They know glass, will wait and see what they think.

Best regards, seachange

[seachange]

A photo would be really helpful!

You may not be seeing 'haze' at all; in asking glass to bend at extreme angles you'll often see 'stretch marks'. It's really hard to know what you're seeing because we may all be using different terms...

Hi Valerie,

Yes, you are right. I am calling them compression marks, because they are inside the sharp fold. One can see multiple tiny striation lines, that all together make the area look hazy.

If not acceptable to the gallery, will have to change the mold to a wider one, where the folds are not so sharp (with this narrow mold the edges of the outside fold almost touch).

Many thanks for your reply.

Best regards, seachange

[Laurie Spray]

What i was saying was a circle of fiber board with a circle of thin fire on top. That way the thin fire turns to dust....no digging out the board.....use it over and over
Sorry if i was not clear. Been out of wack for a few days with a bad case of poison
oak!!