You probably don’t want to forget this step…

Normally after I put kiln wash on a shelf I put it in the oven and let it bake 200 degrees for an hour and then bump it up to 500 for 15 minutes or so to get all the moisture out.  On this occasion I forgot to put a timer on and it ended up baking at 200 degrees for a couple of hours.  I figured this was enough, let the shelf cool down again and then used it a few hours later to tack fuse this project.

The failure to bake it at 500 degrees turned out to be a mega fail.


OUCH!
I figured I could fix it by drilling a hole in the bubble and then taking the piece to slumping temperature.  I flipped it upside down and filled the depression with water.  I cut the hole using a 1/8 inch carbide tipped glass bit and a Dremel moto tool.


Of course one hole wasn’t enough for me.  I was being a bit paranoid and tried drilling a second one because I was worried that the hole would seal up as the glass settled and I’d still be left with a bubble.  The first hold drilled clean. The second one not so much.

But this doesn’t necessarily bother me either since I had planned on putting a layer of colored frit on top and then doing a contour fuse.  I’ll just fill the hole in with frit. Unfortunately the small cracks pictured here weren’t content on staying “small” and grew to split the piece in half.  I’m still pretty confident that I can salvage it and fuse it back together.  The lesson here is you want to make darn sure you’ve got all the moisture removed from your shelf before firing something like this.
Dang! This smarts though…

It was a dark and stormy night…

Well not really.  Sorry.  I couldn’t think of any better way of continuing the-saga-of-the-never-ending-pot-melt.  In the previous episode I rambled about some possible reasons the melt had spider web cracking.  Unfortunately this sight greeted me when pulled the piece out of the kiln.

 

I did more research and found that spider web thermal shock can be caused by the glass sticking to the kiln wash introducing stress laterally in the piece while it was flattening out.  It wounded plausible to me since I found bits of kiln wash stick to the bottom of the melt.  So I figured “Third times the charm; I’ll fire it on a piece of fiber paper and give it a bunny firing schedule”.

BON VOYAGE!

Well…that didn’t work either. So I opted for Plan B…

So what’s the take-home on this?

1. I created a piece to thick to begin with which required another firing to flatten.
2. I made some bad assumptions about how much the piece would thin out and had a cool down schedule that was too aggressive for the thickness of glass.
3. The kiln wash stuck to the glass bottom introducing stress.
4. I used orange glass which I have since learned that it’s one of the colors that tends to change COE under extreme heat.
5. I used some Wissmach glass In the melt and It may not be as well engineered as Bullseye glass and more apt (possibly) to change COE under extreme heat.
6. I used extreme heat – 1650 degrees.

Now many sites I’ve visited say that the glass needs to be heated to 1700 degrees to get as much it out of the pot as possible.  But I’ve also come across may sites (Delphi.com included) that recommend 1600 as the max melt temperature.  One of the reasons being that unless you have a ceramic kiln that is designed to heat to 2000+ degrees 1700 degrees is the generally the max for a glass fusing kiln and those temperatures are extremely hard on it.  I also suspect that a lower temp will also minimize any potential COE shift and that a 100 degree hotter kiln won’t really get that much more glass out of the pot.  So I think I’m go with a lower temp with the next melt and see what happens.

So what about all those pretty shards?

Random form Cabochons!

Alight you may be thinking “OK Jones. This is how crazy people roll; doing the same thing over and over again and expecting the same results”.  Well I’m not that crazy (at least that’s what my therapist tells me).  I tried doing a proof of concept in the microwave kiln to see if would get the spider web cracks.

OK.  It does look a bit fugly since one piece of shard toppled over on the bad side but so far I’m not seeing the cracking.  So I’ll fuse a few of them and set them aside for a while to see if they start disintegrating. 

Thus endith this tale for now.

Blogger Labels: Thermal shock,Sorry,kiln,glass,Wissmach,Bullseye,Delphi,Cabochons

Flattening em out!

I had done a while bunch of cabs using a fiber blanket.  I was having problems with kiln wash sticking to the bottom of the cabs and I was tired of having to clean them off.  I remember reading  on a couple of blogs that “some people” like the texture the blankets lave on the backs of the cabochons.  Well after a few batches I decided that I’m not among “some people”.   Here’s what they looked like.

Pretty rough looking.  OK I picked two of the worst examples; not all of them were this rough.  I decided to try a fire polish to see if that would soften and flatten them out a bit.  Here’s the schedule I used.

Ramp—>Degrees—>Hold

400          1000           20
Full           1325          6
Full           960            45
100           800            0
200           700            0
400           250            0

Here are the results.

Not perfectly smooth but a big big improvement.

How much is enough…

…kiln wash?   I had been doing some research on came across a post that said they mixed the wash to the consistency of heavy cream.  I decided to ignore the directions on the bag of wash that came with the kiln (hey I’m a guy…what do you expect) and mixed up a brew that was twice as thick for my kiln shelf.  After the first firing the wash on some parts of the shelf cracked and peeled up.  On other parts it stayed intact for several firings which resulted in a smooth back for the few cabochons I created.  But alas realized that I had crossed the the kiln wash gods and decided nest time to follow the directions and mix to a 5:1 ratio.  The results were kind of a drag.
Yeah the cabs I created had a smooth back but all of them had kiln wash stuck on the backs of them and I had to clean the shelf off and re-coat.  Not being satisfied with that solution I started to use some thick kiln paper(2mm) I had gotten to see how that worked.  I one sense it worked great because I didn’t have to replace it with each firing.  The downside is that it embossed its own pattern on all the glass I fused. After a few firings I got frustrated again and started to so more research and found there’s really not a consistent answer.  A bunch of people said follow the directions and mix to a 5:1 ratio. Others mixed to a consistency of skim milk, light cream and one enterprising gentlemen mixed it to a consistency where he could use a drywall spatula to apply it.  Check it out.

Now that’s Kiln wash well applying!
By this time I was totally confused.  What’s a poor fuser to do?  Well this is what I decided to do and it seems to be working so far.
For slump molds I follow the directions and use wash mixed to a 5:1 ratio.  For the kiln shelves I use a thicker mix (light cream) and then bake it in my oven at 500 degrees for about 30 minutes.  That seems to provide a good smooth surface that lasts about 3-4 firings.  I addition I got a second shelf so I can have one prepped and ready for when the other shelf gets worn out.