I'm getting trapped air bubbles using hydroperm. I'm thinking that there might be 2 causes.
#1. I am ramping up extremely fast to 1400 after the initial slow heat up to 1000. This is to try and avoid devit. My denver can do it in about 10 minutes which I'm thinking is maybe to fast and is not long enough for the air to escape through the plaster.
#2, I mixed a batch 1.5 part plaster to 1 part water, whipped it up and got a pretty frothy and what I thought was thin mix. So I added more plaster next time, 2 part plaster to 1 part water. got something more like a batter but not frothy and no visible bubbles after the whipping. So maybe if its to thick it wont have the bubbles necessary to make air escape holes?
OK, more description needed here. "getting trapped air bubbles using hydroperm"
what is your mold shaped like? Is this a mold for a bent panel lamp? What is your bending history, yup, I want to know how much bending you have done.
"I am ramping up extremely fast to 1400 after the initial slow heat up to
1000"
This does not matter one bit, bending is a time/temperature realationship, by going too fast,which you are not, you just won't bend the glass as much as if you went slower to the same temp. But that temp is really hot for bending, what glass are you using? and how much detail are you trying to get?
"batch 1.5 part plaster to 1 part water, whipped it up and
this is the mix ratio that US Gypsum recommends, actually it is by weight, did you get a folder of info from them when you bought the plaster? gives mixing ratios, but you don't need it, it is a weak mold for metal casting "one offs" , does you no good for what you are doing.
Give me an idea of the project, but in general, I start with a small - medium mixing bowl, 1/2 full of water,( I don't measure or weigh anything, you don't need to for use with glass for bending, its by eye), then get a scoop of plaster and sort of sift/shake/float the plaster into the water, when it absorbs the water it sinks, just keepshaking the plaster into the water, don't wait for it to sink, it will happen. Try to do it evenly so you get an even layer in the water until there is as much palaster as water, or so it appears, then keep going fo another 1/2 in , about(with practice you get better, the stuff is not expensive, if you miss one while learning, it happens), let it "slake" for a few minutes, not long, less than 5 min. Use a "mixing whisk" from the dollar store to whisk it up and get a good mix, about the thickness of pancake batter, or cake batter, (You do cook don't you?), then apply it to your mold. The first coat on will be really thin, by comparison, to the thickness it will be in a few minutes. At the mixture I gave you , you have about 5 min. working time before it starts to "go off" after which time, you can't mess with it much. You will find out all the tricks the more molds you make.
Those bubbles you were refering to, if they were actually bubbles casused by the glass not dropping far enough into the mold, drill a small hole in the mold at the deepest spot., that will let the air out the bottom, just like the commercial molds., and put the mold up off the floor of the kiln on posts so the air gets out and so tmeperature is even all around the mold.
3 projects. #1 bent panel lamp, typical K11 inserts 11"x6". I have no problem with this.
#2 bent panel lamp, each panel is about 4" by 2", and bent about 1 inch into a bowl shape. they have quit a few dimples slumped into the originals. I am slumping into the mold because the dimple/detail is on the convex side of the glass. but I am getting trapped air and the glass is not fully comming into contact with the mold at the bottom, and I'm not getting the detail on the bottom of the mold. I've fired to several top temps up to 1400 which did not sink to the bottom of the mold. 1450 got close but the glass started to contract. Maybe I should just hold at 1400 for a while. It doesn't seem that the glass isn't hot enough, it seems that there is a trapped bubble at the bottom. I'm about ready to drill a hole, but was hoping that by using hydroperm I could avoid this.
#3 duplicating a textrue of another glass for replacement in a stained glass panel. The glass isn't dropping all the way into the crevices. This is making for a smoother texture.
much detail are you trying to get?
exact detail using several different glasses. Armstrong, Kokomo mostly
Your mixing instructions are just about what I am doing. Maybee I'm going a little to thick with to much plaster. Do you see visible bubbles in the plaster when you are done?
Ya I'm going to try that, but that doesn't help with the glass sheet texture in project #3.
they have quit a few dimples slumped into the originals. I
OK, drill a tiny hole, or 2, to let the air out, don't know why air WOULD go thru the plaster? I alwayd drill holes in the deepest spot on a slumping mold, whatever the mold is made of. Blanket is ok, but all plasters get a hole, and then you will find you don't need to go as high in temp either, that was hot air holding the glass up, not a bubble formed by anything foreign. 1285 should be high enough to get that to drop into a mold of that size and shape, and pick up the dimples too. If there are several deep spots around the dimples, drill several holes, by only going to 1285 you are not going to have any problem with a hole.
and I'm not getting the detail on
Why avoid it? You don't see any sign of it on the glass as long as you don't go to those extreme high heats for bending?
drill holes worked great. But I was under the impression that using hydroperm I wouldn't need to do this, no that it's a bid deal. Anyways, worked great and lamp looks great. by the by, it was a Handel Similar to
I don't know where the idea that you wouldn't have to drill holes with Hydroperm came from? Deep depressions always need it, but in bending that particular shade, I usually fire twice. One slumped in to get it started, and then draped over to show the "ridge". and let it form , If you look at the original, usually there are mold marks on the inside, there are other ways too.
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