WarmGlass.com

Hi, I have to confess I have one of those microwave kilns, the Magicfuse. I'm sorry. It was an experiment and I could not spend a lot up front.

What I want is to make cabochons by fusing little piles of frit. (I need them in precise sizes which molds don't come in, and so far it seems like the best way is by weighing out the frit.) After a lot of under- and overheated experiments it's *almost* working: I'm getting nice round uniform fuses, except they don't separate well from the base.

If I use shelf paper it seems to crawl up the sides of the cabs, leaving a scuffed texture that takes forever to pumice off. But I can't spend forever on these, and they still don't look perfect afterwards.

If I use kiln wash -- 5 coats brushed on with a haik brush, dried with a heat gun, sanded lightly -- the cabs form clean but they stick, each one pulls off a patch of wash plus a layer of the kiln base. I can scrub the wash off the cabs and they are OK (hazy on the bottom but I don't need the bottom to be clean) however if I keep doing this the kiln base will soon be too pockmarked to use. And I feel like I'm wasting my time with the wash: isn't this outcome exactly what it's supposed to prevent?

Should this work? Any idea why it isn't working? Suggestions?
Occasionally I get a single cab that is clean and all over, like the ones I buy commercially. So I feel like it should be possible.

Answers of the form "buy a real kiln" will be noted but are not the most useful thing right now. I will when I can, but I would be able to afford that sooner if I could make this work.

Thanks,
Bathsheba
http://bathsheba.com

Try using a piece of shelf paper a little larger than the pieces you are firing but put a "weight" like a kiln post or scrap glass on each corner to hold it down. That way it won't roll up on your pieces.

vblue wrote:Try using a piece of shelf paper a little larger than the pieces you are firing but put a "weight" like a kiln post or scrap glass on each corner to hold it down. That way it won't roll up on your pieces.

Thanks for the reply!

I've been using a bigger piece of paper, carefully flattened, with 6 or 8 cabs on it. I could add some weights as well, but given that it's already coming up on all sides of all the cabs (i.e. it's not just one piece in the middle of the paper, or just the cabs near the paper's edges) I'm not sure more would make a difference?

I don't know much about microwave kilns but I suspect a few things are occurring. First of all, since you don't have much control over the heat of the kiln, you're likely over-firing, which makes kiln wash stick.

Then, you're firing frit, which requires more heat for the bits to pull together and create a single mass of glass, and probably causes the shelf paper to curl up as the glass moves.

I'm guessing you're using some opals, which tend to stick to kiln wash more than transparent glass.

A few things I'd try: eliminate the shelf paper, and apply several thin layers of kiln wash. Try making your pieces with a base of thin iridescent glass, with the irid side down, which will release cleanly and not stick to the wash. Play around with the time in your microwave to either reduce the heat a little or shorten the time. You want to the glass to achieve your desired results in the minimum amount of time at its top temperature.

And remember, the bottom of all fused glass will have some texture.

maybe try a different brand of kiln wash. I use Hotline Primo and have this problem a lot too. people have told me this brand does that.

Bathsheba, I visited your site - OMG what fun! In addition to skills in math and metal you are a bit of a wordsmith too. Carry on!

Thanks guys!

@valerie I agree that it could be overfiring, I'll try a bit shorter and see if it helps. The glass is glow frit, which I don't know if that counts as "opal", but certainly it isn't clear. You make a good point that I could use a thin base layer of something else...I don't mind texture on the bottom, I just want it to stop tearing up the kiln base.

@lorimendenhall People do seem to say Primo is difficult to use. I have Paragon separator, but maybe worth trying some others!

@Vonon Aw, thank you. 3d printing is so monochrome, though -- I've had glass envy forever!

bathsheba wrote:I agree that it could be overfiring, I'll try a bit shorter and see if it helps. The glass is glow frit, which I don't know if that counts as "opal", but certainly it isn't clear. You make a good point that I could use a thin base layer of something else...I don't mind texture on the bottom, I just want it to stop tearing up the kiln base.

But note that I didn't suggest a base layer of 'something else', I suggested iridescent glass with the irid coating face down on the shelf. The coating acts as a separator and isn't know to stick to the shelf.

Agree with Val--use the least heat possible to get this to work, and if you can cut perfectly uniform squares of thin irid, put them irid-down on the shelf. Top with a smaller amount of "glow frit." When it melts, it will pull together into a cab.

Besides the irid base preventing some of the sticking, it may also allow you to reduce the heatwork a bit--you've now got solid glass next to shelf, where there's more insulation and less heat--and that would also help with sticking.

Point taken. I'll try it when I can get some thin iridescent glass. Have to get together the next order...one thing is that .

One other question I had is, do you think could COE make a difference to how much it sticks? I have glow frit in 90, 96 and 104 (from Sundance and glowglass.com, but I think the guy at glowglass is making all of it), but other than not mixing them I haven't been paying too much attention to which is which.

Thanks again! It's great to have things to try -- I hope to do a couple of fuses tomorrow and see what happens. ^_^

I don't think the COE makes as much difference as color and opacity, although if it's a softer glass it might be more affected by overfiring.

FWIW, I just overfired one of my kilns, again. About ten small samples 3 mil. flashed glass, which were supposed to go to 1310 F with a five minute hold (to clear the etched areas of the flashed glass), went to 1850 F and held there for possibly 30 minutes, when I switched it off. That's the bad news.

The good news is that none stuck to the shelf. As frequently recommended by Bert, I use alumina hydrate. I use it in its powdered form, not as a wash. All the samples, which started as approx. 2.5 inch squares, rounded up into 6 mil blobs with the colour scattered on the surface. Needless to say the etched areas were really clear.

I didn't examine the undersides of the blobs but they felt smooth. I'll check and report.

( Kiln is now connected to empty channel on controller, new pyrometer, new sending unit and is behaving itself as it should again. Will try to determine the cause of the misfiring later.)

Anyway, I really like firing on alumina hydrate and use it over and over again, just smoothing it between firings. It wouldn't work on sloped surfaces but does well on a flat surface which is what I need for painting and firing. Hope that helps someone. Jen

I checked the underside of the blobs....they all have alumina hydrate embedded in the bottom, but they did go to at least 1850 F and held there for 30 minutes, however the shelf didn't suffer which I'm sure it would have done with kiln wash. I've since fired more glass on the same bed of alumina hydrate, at the right temperature, without any ill effects. I recommend it! ( BTW I don't own a mine, this is an objective endorsement!) Jen

Jen how do you smooth the alumina hydrate? I know it is a powder and even if spread thickly I can't imagine getting it smooth again.Georgia

Georgia, I use an old rolling pin. (I believe it's actually a kitchen utensil but can't imagine how one would use it. No flat glass in the kitchen ) The AH seems to absorb moisture in humid weather so tends to clump a bit when sieved on.

I used to use whiting, (calcium carbonate), smoothed by hand over a section of folded newspaper, as taught by Albin Elskus. When I bought a used kiln it came with a 25Kg pail of Alumina and I noted that Bert used it so made the switch since I had it on hand. The whiting worked fine for painting and firing, too, but I don't know if it will stand fusing temperatures, or would have withstood the recent 1830 F meltdown.

Using it at painting and firing temperatures I don't fuss if there are some small divots in the surface as the glass bridges it without sagging into them. (Bert has published his formula here on the WGB for making an AH-based liquid kilnwash.)

If I reuse a shelf immediately after a firing cooldown the AH flattens more easily and doesn't stick to the roller, presumably because the moisture has evaporated. If I needed a perfectly smooth surface I'd probably prefire some to a low temp. with the kiln cracked open before rolling it out.

In a PM I was cautioned to use a respirator. I agree that would be a good idea, especially if it's dry and powdery. As mentioned, the humidity here means it
doesn't seem to be getting airborne. I'm going to check that by putting some black cardboard alongside the next shelf I sieve AH onto.

A quick check on Wickipedia suggests it may really be alumina hydroxide but I'm not curious enough to read all those scientific papers.
Jen

Jen, thank you for all the information.

I do much the same thing with plaster of paris. I tend to use a broad spackling knife to flatten mine, but a rolling pin is a cool idea.

[quote="Morganica"]I do much the same thing with plaster of paris. I tend to use a broad spackling knife to flatten mine, but a rolling pin is a cool idea.[/quote]

i use a wine bottle with the neck cut off. no handles on the ends to run into the kiln walls.

So the benefit of using a sifting of alumina (or similar) is so you get the separator effect without the conversion thing that kiln wash goes through that results in it's becoming caked and chippy? So what is the downside of that choice that has us using kiln wash or shelf paper?

Downsides are : dusty, fussy, cant reposition work. You can get around that by mixing alumina with a binder (cmc, elmers glue and water) and using as a wash. My wash is 80 : 20 alumina : kaolin. Soft but reusable. I generally refresh with a coat or two and fire multiplr times. I scrape only when it gets chippy /bubbley .r.