Advice on what went wrong

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roykirk
Posts: 18
Joined: Tue May 12, 2015 9:54 am

Advice on what went wrong

Post by roykirk »

This is an experimental project I've been working on over the past few days. I'm somewhat satisfied given so many unknown variables, but clearly I need to tweak the process a bit to fix a few problem areas. I was using pieces of tempered red translucent "fire glass" for this project with an unknown COE. The mold was a 50/50 POP & silica flour. Rapid ramp to 1650F, hold for 30 minutes, then allowed to cool to room temperature over about 8 hours. Here are the photos:

https://drive.google.com/open?id=198GIi ... VWxrkPpRhy

1. I was slightly disappointed that my nice translucent glass shards turned opaque during firing. I've never experienced this before when using translucent glass.

2. Hole on the left side of the face. I'm assuming this is from an air bubble that developed when the glass was molten and it didn't have a chance to rise to the top of the mold before cooling. I'm not quite sure how to avoid that in the future.

3. Strange raised "ridge" that formed across the face during firing. It's about .25 mm high and clearly visible in one of the photos. At first I thought it was a crack, but closer examination showed it's definitely a ridge. There was no such feature in the mold, so I'm mystified how it formed.

I'm pleasantly surprised that not a single crack formed in the piece given the lack of using a firing schedule and the unknown COE of the glass.
Judd
Posts: 295
Joined: Mon Sep 01, 2003 9:45 am
Location: Arkansas

Re: Advice on what went wrong

Post by Judd »

1) You didn't program an anneal into your firing?
Well, that screwed up your piece.
2) Unknown COE glass? That's why the red went opaque. It's not formulated to go to high temps, and reds/ oranges are prone to turn opaque. You can cast at lower temperatures. I cast at 1465. Also, use tested Fusible glass. Furthermore, was this glass all from the same sheet? I saw the pic of the glass pieces, and in the finished piece some areas appear darker, while others opaque and some translucent. You may have mixed uncompatible glass.
3) The cheek bubble - too fast at heating up/ cool down, you didn't anneal...
4) The ridge - probably a crack or ridge that was in your mold or a ripple when you put your Kiln Wash on the mold.
5) Not a single crack? Maybe your glass was thin enough and able to anneal, but I doubt it will survive due to a lack of an anneal cycle.
roykirk
Posts: 18
Joined: Tue May 12, 2015 9:54 am

Re: Advice on what went wrong

Post by roykirk »

Thanks for the tips, Judd. Right now I don't have a programmable kiln, my good one having died over Christmas. All I have to work with at the moment is a Skutt kiln with a limitless dial. But I'd rather be firing something than not, so I decided to give it a go the best I could and see what happened. The best I can do for annealing is to dial it down more slowly next time and see if that improves things.

There's definitely not a single (visible) crack anywhere in the almost 1.5" thick piece. I suppose there could be somewhere deep inside but I'm just not seeing it. Perhaps that's a good part of the piece ending up opaque. :D
Kevin Midgley
Posts: 773
Joined: Mon Mar 10, 2003 11:36 am
Location: Tofino, British Columbia, Canada

Re: Advice on what went wrong

Post by Kevin Midgley »

wear a kitchen timer on your shirt to remind you to go and check the kiln. #-o
roykirk
Posts: 18
Joined: Tue May 12, 2015 9:54 am

Re: Advice on what went wrong

Post by roykirk »

Kevin Midgley wrote:wear a kitchen timer on your shirt to remind you to go and check the kiln. #-o
Oh, I check it regularly. About every 10 minutes. Didn't mean to give the impression I'm just turning it on and walking away.
Kevin Midgley
Posts: 773
Joined: Mon Mar 10, 2003 11:36 am
Location: Tofino, British Columbia, Canada

Re: Advice on what went wrong

Post by Kevin Midgley »

That was the point.
If you want to fire pieces like that manually, you need to be reminded and wearing the timer does it.
About 10 minutes will tend to not give you repeatable consistency.
Judd
Posts: 295
Joined: Mon Sep 01, 2003 9:45 am
Location: Arkansas

Re: Advice on what went wrong

Post by Judd »

Roy,
Your kiln died? Ah... sad panda.
Get that bad boy fixed. It's much cheaper to fix a kiln than buy a new one.
What's the problem with the kiln. Many times a repair is quite cheap.
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