Evening thickness of glass after a pot melt

[baxters]

 

How can I even the thickness of a dammed pot melt piece of glass? 3/4 of the edges of the circle of the pot melt are about 1/2 inch thick, the other quarter is about 1/4-3/8 inch thick I used a level prior to firiing and it seemed to be level. Can I just rotate the glass and add a little more glass to the pot right above that section and refire to 1700 with the steel dam? Or remove the dam and fuse fire to 1500? Do I add glass or will it even itself out on it’s own?
Thanks. This is the third pot melt in 4 days and it is the best one yet. I really want to slump it into a bowl but the thickness is way off.
Susanne

[Stephen Richard]

Your post shows you know the need to have a level shelf.  However your results show the shelf was not level.  You need to check levels on the “vertical” and “horziontal” as well as the two diagonals.

You also need to consider whether your pot was centred over the dammed space.  If it wasn’t then you will have more glass on one side than the other, unless you had a very long soak at the melting temperature – ca 950C.

If your disc is 13 mm at one side and 6 mm or 10 mm at the other you have a more complicated reheating problem than a simple 10 mm or 13 mm all over disc.  The thin side will heat through more quickly than the thick side.  In any case the centre of the disc will be thicker than the sides. So you need to slow the initial rate of advance beyond that for even 13 mm.  I suggest adding the difference of the thicknesses to the thickest part to get an indication of the schedule you should run.  In this case 6 form 13 is 7, which added to 13 gives a schedule for 20mm glass.  This may seem conservative, but if you are trying to save a piece conservative is the way to proceed.

Secondly, to get the glass to flow easily you will need high temperatures again.  This may begin to give you problems with compatibility.  So my suggestion is to use full fuse temperature only, but soak for several hours, maybe up to 4.  This will give you problems with devitrification, so a borax spray or other devit spray is advisable.

This is not a simple problem, but if you are successful it it will prove very satisfying.

 

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

[baxters]

I had one pot in the center as well as two on either side- I center pot was large enough to hold the amount of glass I needed. Before I fired I was concerned about that.
I now understand the need for a slow advance and how you came up with that.
3 more questions:

Can I do this on thin fire paper since I am firing to 1500 or do I need to prepare the shelf as I did for the pot melt?

Do I need to go on and remove the kiln wash that is on the underside on the piece?

Do I need to dam it again? ( I think yes). I am so afraid to fire that thick a piece w/o one and I have never done a pot melt w/o one.

My firing schedule for this piece was
600/1000/20
250/1100/20
450/1700/90
9999/1540/45 then to 900/120 and a conservative cool down

The first two this week have alot of popped bubbles on surface, not over an 1/8 diameter. Do I refire with top side up to a full fuse1500 with a dam? Using thin fire or heavy kiln wash? Thickness 1/2 inch.
Or do I flip it over and fire to 1500. I would guess at a soak of 30 min
The need to redM is always confusing to me. Thickness again is 3/8 on one and 1/2 on the other

The firing schedule on the ” bubbled” pieces were pretty much the same except 700/1700/90 & soaking at 1500/60

I really appreciate your good explanations and advice. It is nice to know these forums are here and people are so willing to take the time to answer these questions.
Thanks
Susanne

[Stephen Richard]

“I had one pot in the center as well as two on either side- I center pot was
large enough to hold the amount of glass I needed. Before I fired I was
concerned about that.”

My question was about the centring of the pot above the circular dam.  If not centred, It can leave you with more glass on one side than the other, if the high temperature soak is not long enough to  allow a flow to equalisation.

“I now understand the need for a slow advance and how
you came up with that.”

OK. Good

“3 more questions: Can I do this on thin fire paper
since I am firing to 1500 or do I need to prepare the shelf as I did for the
pot melt?”

I don’t now how you prepared the shelf, but by implication, you used batt wash.  If so, yes you could use thin fire or a new layer of batt wash.

“Do I need to go on and remove the kiln wash that is on the
underside on the piece?”

Yes.

 

“Do I need to dam it again? ( I think yes).”

Yes if you want it to be the same size.

“I am so
afraid to fire that thick a piece w/o one and I have never done a pot melt
w/o one.”

The major danger is that there will be too much glass and it will overflow the shelf.  But there is a good pot melt calculator on this site (under tools, I think) that will tell you how much glass you need to get a disk of given dimensions.  I do all my pot melts without dams.

“My firing schedule for this piece was 600/1000/20 250/1100/20
450/1700/90 9999/1540/45 then to 900/120 and a conservative cool down”

333C/hr seems a bit fast for the ceramic pot, but if it is surviving, fine.  The 20′ soak at 538C seems odd and unnecessary. Why you slow down to 140C/hr for 55C after 538C is also a mystery to me. If you want a soak to let the air out from between the glass pieces, this should be done in the region of 650- 677C with a soak of ca. 30mins.  In general people speed up as the glass gets warmer.  You seem to be slowing and then speeding up, but not to your initial rate of advance of 333C/hr.  Odd.  I think 838C (1540F) is too hot for your equalisation temperature, try your full fusing temperature instead.  I would use the Bullseye schedules for annealing thick pieces and go from your equalisation temperature afap to 482C and then apply the schedules.

“The first two this week have alot of popped bubbles on surface, not over an 1/8
diameter. Do I refire with top side up to a full fuse1500 with a dam?”

A good strategy is to clean the bottom and turn it over and fire, although I would normally not go much above a fire polishing temperature.  In this case you will want to go high enough to allow the glass to flow.  This means that more bubbles will appear and break on the surface.  It is part of the nature of the being.

“Using thin fire or heavy kiln wash?”

You can use either, although in this case I would use batt wash as you want the glass to move and that might pull the thinfire into the glass.  I – unlike most people – do not use thick layers of batt wash.  I spray the wash onto the shelf until it is uniformly pink.  This is not very thick.  All you are trying to do is to keep the glass and the shelf separate.

“Thickness 1/2 inch.”

?

“Or do I flip it over and fire to 1500. I would guess at a soak of 30 min”

I think you are asking whether to clean the present back, turn it upside down, dam and then fire slowly to 815C.  If so yes, but you will need a much longer soak to allow the glass to move and become approximately the same thickness all the way across.

“The need to redM is always confusing to me.”

Just as using the imperial system is to me.

Thickness again is 3/8 [10 mm] on one and 1/2 [13 mm] on the other.

So the difference is 3 mm (not the 7 mm you indicated it might be)  This means that you could fire as for 15 mm [5/8 inch].  This would mean an initial rate of 90C/hr to 250; 115C/hr to 500; 150C/hr to top temp. [no bubble squeeze required].

“The firing schedule on the ” bubbled” pieces were pretty much the same except

700/1700/90 & soaking at 1500/60″

This would indicate to me that you have not yet settled on a firing schedule.  Are you keeping notes so you can compare the results of different firing schedules on different amounts of glass and of different colour combinations?

“I really appreciate your good explanations and advice. It is nice to know these forums are here and people are so

willing to take the time to answer these questions. Thanks Susanne”

 

Also note that unless you have your shelf perfectly level, the same un-eveness will occur again.

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

[baxters]

Please review my firing schedule:

200/1000/15-I want to go as slow as possible so it won’t break.

200/1250/30 to make suree all glass is at the same temp

300/1500/ 4 hours long hold to allow glass to move to same thickness

9999/900/2 hours

50/800/00 for a slow cool down

100/400/00

off

OR

200/500/00

250/1000/00

300/1500/4 hours

I’m still not sure if i should have a hold time 1250.

I’ve cleaned it, flipped it(placed top side on the shelf, and leveled the shelf . Ready to fire. I will to hear your comments on the schedule though!

Thanks again. And I am keeping a log. Susanne

[Stephen Richard]

“Please review my firing schedule:

200/1000/15-I want to go as slow as possible so it won’t break.”

I believe you said your piece was 12 mm at one side and 6 the other?  If so the initial rate of advance could be 90F to 500F; 125F to 985F (no soaks at either); 160F to top temp.

“200/1250/30 to make suree all glass is at the same temp”

This is a bubble squeeze temperature.  If the rate of advance is slow, no soaks are required to get the glass at the same temperature throughout

“300/1500/ 4 hours long hold to allow glass to move to same thickness

9999/900/2 hours

50/800/00 for a slow cool down

100/400/00

off”

This is certainly slow enough

“OR

200/500/00

250/1000/00

300/1500/4 hours

I’m still not sure if i should have a hold time 1250.”

No soak at 1250F is required for this piece if you use the slower rates of advance given above.

I’ve cleaned it, flipped it(placed top side on the shelf, and leveled the shelf . Ready to fire. I will to hear your comments on the schedule though!

Thanks again. And I am keeping a log. Susanne

Best wishes

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

[blamdimond]

I have had screaming success with the following schedule;

425   1000   5

400   1100 10

full    1600    50

full     1500    20

full      950    2.00

300    300    0

Here is the fail part…I also did a Bullseye pot melt,(obviously a different anneal temperature),  FYI royal blue takes over everything!  Seriously.  Oh, and so does adventurine blue.  You would think I would have learned my lesson.  Oh well, I’ll just pot melt it again.

I believe I had about 3 pounds of glass, as my result was around 10″ or so.

[blamdimond]

Forgot to add this…if you live in Canada…there are wonderful terra cotta pots at Zellers.  They are made in Germany, and are reasonably priced!

[Stephen Richard]

On this site ( under tools, i think_) there is a spread sheet to help you calculate how much glass is required for defined diameters and thicknesses. Provided by the Host of this site.

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

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