pot melt help needed

[Doris Sisk]

I have done a lot of research on this board for info on pot melts. I have now done two with bad results and I hope someone has a brilliant answer for me!
I am using a 6 in. terra cotta pot with about 2 pounds of glass (the colors come out fine). I place it up about 5 inches across cut tile shelfs. I also have made the whole in the bottom of the pot larger - to about 1 inch. I melt it onto a shelf coated with about 14 coats of kiln wash.
I'm using Spectrum 96.

My firing schedule is:
700 - 1650 -30
AFAP - 960 - 60
250-920 - 60
500 - 700 - 0 - off

My pieces have many small - medium size bubbles and even worse, they both have cracked. Not in the middle, but near to one edge.

I got the firing schedule off of this board and I've always had good luck with other suggestions from you talented people.

Anyone know where I'm going wrong? Thanks.

[Lisa Allen]

You might try going slower from 960 to 700. I would probably go no faster than 100 dph with no holds.

it is my understanding that what you want for proper annealing is a slow and steady descent through the annealing range (960-700). The hold at 960 is just to make sure that the temp of the glass is consistent before starting that descent.

Lisa

[DonMcClennen]

To eliminate bubbles try 1670 F for 45 min.
Don

[paulfjackson]

I Agree. Soak longer (bubbles), descend slower (cracking).

[Doris Sisk]

I appreciate the input. It will probably be a couple of weeks before I am able to try a pot melt again. Thanks.

[Rob Morey]

Doris,
That is the firing schedule that I use for my Bullseye glass. Spectrum could be different. One thing though, hold longer at the top, 1650 or so for an hour and then add another soak for 30 minutes at 700 then off. See if that helps. Like everyone else said, slowing down from 920 to 700 couldn't hurt.


Rob

[KellyG]

I've had some successes and some failures with pot melts (same schedule for all). The failures resulted in cracks (days later) STRAIGHT down the middle.

I now wonder if temps. >1600 for extended periods can affect compatibility.

...K

[Brad Walker]

Yes, high temps for extended periods of time can affect compatibility. I try to minimize this problem by going higher and for less time.

You should also check your annealing schedule. Annealing problems are also likely to show up after a few days.

[Jerry]

Well, I know a little bit about pot melts and have a couple of suggestions you might try.

Your fractures may, or may not be annealing issues. Melting directly onto a shelf invites disaster regardless of how many coats of seperator you put on because the glass tends to move the seperator around and stick to the shelf; there are better ways.

I'd begin by asking you what you are trying to accomplish? Do you have a shape in mind? I find it's hard to achieve a particular result when I don't know what the result I'm looking for is. So, here's a recommendation; you are already using flower pots, try melting into a flower pot tray! They come in a variety of sizes but the 8" seems to be the most popular and easiest to find. Scrub it well until water soaks and evaporates evenly. Coat with several (three) coats of seperator. Now, while the seperator is still wet, sift a coating of talc, or silica, or as a last choice, plaster. The wet seperator will hold this sifted layer in place and aid in keeping the glass off the clay pot.

I use a base sheet in the tray onto which I melt. That helps distribute the glass more evenly plus stops the movement of glass on the seperator stuff. The result is no garbage on the back of the piece.

Now, as to the amount of glass you use, it's the old formula that you can't ever remember when you want it; Pie R Square (Yeah, I know, pie are round and CORNBREAD are square). For your 8" pot, 4 is the radius, the "R" part. So, 4 x 4 = 16, times Pie. To make the numbers easier, I usually cheat and use 3.2 as pie. So you end up with 51.2 square inches, well, round inches unless you are using a cornbread pan. Now, that won't get you far because you want a thicker piece, so I tend to double that number or even tripple it and that's the square inches of glass I need in the pot. If you know how thick the piece will be, and this formula will tell you that, you can figure out the annealing times a lot easier.

Now, I use Spectrum series 96 and non series 96 in the same melts; remember, the glass moves a lot and that helps stop devit. If it happens, refire flat with spray and it all goes away.

I like to go a bit hotter than most; 1700 with a two hour hold. That does two things; melts ALL the glass out except for a trace, and allows the disc to flow out evenly in the tray. Cooling is pretty direct; fast to 1000, hold for one hour to stabalize everything, drop to 960 for 5 hours and go to 600 at 50 dph. That takes you through the danger areas pretty well.

If all that doesn't confuse you, let me know and I'll try again.

Good luck,
Jerry

[KellyG]

Great information Jerry! Thanks for posting.

...Kelly

[charlie]

I use a base sheet in the tray onto which I melt. That helps distribute the glass more evenly plus stops the movement of glass on the seperator stuff. The result is no garbage on the back of the piece.

Now, as to the amount of glass you use, it's the old formula that you can't ever remember when you want it; Pie R Square (Yeah, I know, pie are round and CORNBREAD are square). For your 8" pot, 4 is the radius, the "R" part. So, 4 x 4 = 16, times Pie. To make the numbers easier, I usually cheat and use 3.2 as pie. So you end up with 51.2 square inches, well, round inches unless you are using a cornbread pan. Now, that won't get you far because you want a thicker piece, so I tend to double that number or even tripple it and that's the square inches of glass I need in the pot. If you know how thick the piece will be, and this formula will tell you that, you can figure out the annealing times a lot easier.

how does using a base piece of glass affect your thickess and volume calculations, since it would try to even out to 6mm thick? also, how does the clear class affect the look of the back? does it get pushed outwards, or does the dripping glass ride over it and spread out evenly across it?

[Jerry]

Charlie,
Obviously the base sheet enters into the volume calculations, but it's easy enough to calcullate it. Once you determine the total amount of glass necessary to get the thickness you want, subtract out 1/3 of it for the base sheet. And, remember, I'm using a containment vessel so the glass CAN'T level out. I wind up with a uniformily thick disc.

You may use a clear piece for the base sheet as you wish. It will be textured because of all the stuff in the vessel, but we are looking for translucency rather that transparency and the texture helps all that. The glass in the pot tends to slide across the base sheet so you wind up with a clear, textured piece on the bottom. It's a nice effect.

Jerry

[Redfisher]

I can't find an answer in any searches. What light box bulb do I need to look for fractures?
I have a puece I took out of the kopn and I heard a couple of tink sounds foming from the directtiom of the piece.
Thanks in advance!
Terri

[Stephen Richard]

Any light bulb. Put the glass between layers of polarised light filters. The steress will show up as light areas.
Method here:
http://glasstips.blogspot.co.uk/2009/07 ... lters.html

[Havi]

Instead of zillion coats of primer, I use a layer of 3 milimeter fiber paper.
I learnt it from one of the better guru's of this board.
This also creates the kind of textured back which allows better 'game' of the light thru the piece.

Due to a fracture at one of my first melts - I do mostly MESH melt, not pot melt - I do not stay long at 1700F, but stay for a while at 830 Centigrade. when going down, and of course a conservative annealing.

Something else I found out is, that when I fire the melt again - fuse it to another piece - it 'opens' becomes bigger, and the circles which had been on the melt become bigger.. I am not sure I am being clear on this. But the outcome is quite attractive -for me and for others who see this.


Havi
ps I suspect that the fracture developed - in my piece - was because of a longer stay at 1700, and change of viscosity of one of the glasses, which lead to lack of compatability. Since I stay shorter period at 1700 - it never happenned again, not even while boiling the glass which is at the same temp.

[Redfisher]

Any light bulb. Put the glass between layers of polarised light filters. The steress will show up as light areas.
Method here:
http://glasstips.blogspot.co.uk/2009/07 ... lters.html

Thanks soo much!