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Help! I got this Poinsettia Texture Frit Bowl mold and am getting a bubbling problem.

I put down the frit and capped with 2-3mm 11" circles of Texta glass. No frit in the center. I had a huge bubble in the center only. So I put scrap Texta into the middle and refired. Now I have 3 bubbles.

Mold was primed with multiple coats of MR-97 and cured at 200° for 20 mins. First firing had some of the mold detail break off into the glass. Mold got 3 more coats an another curing before second firing.

Firing schedule:
300/1150/00:15
50/1250/00:20
850/1450/00:15
AFAP/950/01:00
80/750/1:00
400/120/00:00

My kill is a Paragon CS-14D. I put the mold, by itself, on top of four 1/2-inch posts on the bottom of the kiln. I only have 6-inches of space in the kiln.

I have no idea what I'm doing wrong. I do have enough frit and Tekta to try again, as soon as I get some good advice.

Questions: Should I pre-fuse the two 3mm Tekta caps?
Should I NOT pre-fuse but instead cut it or break it up?
Should I drill holes in something somewhere?
Should I fill the center area with Tekta frit?

Too fast from 1250 to 1450. Slow down to 250dph. Wouldn't hurt to lengthen the hold at 1250 either, but slowing down the rate from 1250 up is the major reason for the large bubbles. Depending on your kiln, you might need to go a little hotter than 1450 also.

Prefusing the Tekta cap (or, even better, using 6mm Tekta) would also help. Not necessary to use coarse clear frit or broken up glass instead of solid Tekta.

Use three posts under the mold. Make sure the posts are all the way at the outside of the mold (i.e., half sticking out), rather than directly under the mold, which can cause uneven heating.

The post positions may have something to do with it. I know for a fact that I put the posts several inches inside the diameter of the plate. I still have the plate/mold/posts exactly where I fired them. I'll take a look in the morning. Pre-firing the 11" disks into one double-thick cap will be part of the next firing. I wish I could get ahold of double-thick from my supplier. This will slow my process, but maybe I'll get it right next time.

I'll also follow your advice on the ramp speeds and hold times. Would going from 20 to 30 minutes be enough at 1250? That's 50% more.

Sure seems like there's a lot of trouble with these molds!

By not having any frit in the center, and then placing two Tekta rounds on top, you essentially created a large air space, that had nothing other to do than blow a bubble.

Follow Brad's suggestions, and for the next one, try a design where you don't leave large voids.

BillsBayou wrote:The post positions may have something to do with it. I know for a fact that I put the posts several inches inside the diameter of the plate. I still have the plate/mold/posts exactly where I fired them. I'll take a look in the morning. Pre-firing the 11" disks into one double-thick cap will be part of the next firing. I wish I could get ahold of double-thick from my supplier. This will slow my process, but maybe I'll get it right next time.

I'll also follow your advice on the ramp speeds and hold times. Would going from 20 to 30 minutes be enough at 1250? That's 50% more.

Increasing to 30 minutes should be enough. The slow speed from 1240 to your top temperature is the most important factor.

Here is a blog post of mine on using a poppy mold. This is not the same mold, but it is similar in concept. Some of the info here may help.

http://jestersbaubles.blogspot.com/2015 ... ppies.html

Dana W.

That is a wonderful PDF on the mold set up. Well done. AND if you are worried about bubbles, try sprinkling clear frit evenly over the layed down colour frit. You will get NO bubbles that way. Les