Baked on Kiln Wash

[callidesigns]

Hello All,

I am new to the forum and have searched previous posts for an answer, but still yet remain puzzled with my problem. I knew better than to fire twice on one kiln washing, but did it anyway--following a discussion with someone else who does so. I use primo primer and coated the shelf with 6 coats. The fired glass pieces all wound up with kiln wash baked on the back. I have tried to remove with vinegar (got all white kiln wash off) but what remains is what looks like etching or devit. Here are other remedies I have also tried, muratic acid, wash away, lime away, steel wool---yet nothing touches the etched look. Are these pieces doomed for hammerville, or does someone have a solution. (I have no sand blaster)

Thanks for an answer,
Connie

[Morganica]

Well, first of all, depending on the kilnwash you're using it can be perfectly acceptable to fire on it more than once. There are kilnwashes made to be used once, scraped off and reapplied, but that's always seemed like a lot of extra work for not much gain (to me, anyway).

But if the kilnwash is sticking on a new application, it could be that:
--You're firing too hot. If your top process temperatures pass 1500F that is more likely).
--Your kilnwash layers are too thick.
--You've got a pale opal glass on the bottom; kilnwash will stick to an opaque glass--especially a light-colored opaque--than a transparent glass. If you can avoid putting those glasses on the bottom that can help.
--The kilnwash went into the kiln wet. It needs to dry between coats. A lot of people kiln-dry their kilnwashed furniture with great success; I've found that if I heat the shelf past about 180F to dry it, the kilnwash doesn't last as long. If I've time, I prefer air-drying.
--Or other reasons I can't think of at the moment.

Without looking at good pictures of your glass it's a little hard to tell what's happened, but it sounds as if you've etched the glass in getting the kilnwash off. I've used some of the things you've tried and they will abrade the glass if left on long enough. You might also have some devit, but from your description I'd suspect not.

Either way, once the surface of the glass is mechanically/chemically altered it needs to be polished to restore the shine. You can firepolish it--clean it very, very well first to make sure there's no residue of kilnwash or cleaner left on the glass--or you can polish it by hand. Or a combination of both.

A sandblaster is wonderful for such things but you don't really need it--diamond handpads are relatively inexpensive and take less time than you think. Or go to the hardware store and buy a plain old sponge and wet-dry sandpaper.

[Brock]

--The kilnwash went into the kiln wet. It needs to dry between coats . . .

Not in my experience.

[callidesigns]

Thanks for your feedback, Morganica.

Here is a pic of what I am talking about (Not sure if I understand how to send the picture, so here goes a good try). I am using 6 coats of Primo Primer and this was the second time I fired on the same kiln wash application, so it was completely dry. The etching was actually there, prior to using any of the removers. I am thinking it is caused in part by the PRIOR piece that was fired, which was white opal glass, so what you mention makes sense. The piece that is in the picture was fired at 1470F which seems reasonable, but maybe I am wrong. At any rate, looking at the picture--can you tell if it will fire polish, now? If not, I will use the diamond hand pad and as a last resort, find a nearby sandblaster to use. Making a new set would likely be a lot simpler!

[Morganica]

--The kilnwash went into the kiln wet. It needs to dry between coats . . .

Not in my experience.

If I stick a bunch of glass on wet kilnwash, take it up to fusing temps, I get a higher rate of flaking and sticking. I've always thought it was because the glass trapped moisture/steam underneath and loosened the kilnwash, but I don't know if that's the agent or not.

And if I don't let the kilnwash dry at least a bit between coats, I just wind up dissolving the old kilnwash in the new...or making it too thick when they blend together. That doesn't happen for you?

[callidesigns]

I apply a coat of kiln wash, then dry with hair dryer, apply the next---dry with hair dryer, until all layers have been applied, so it doesn't happen to me. The finished product is very smooth and never flaky. The first piece I fired came out beautifully with no residue. The next day without re-applying new kiln wash, I fired the project that you see in the picture. I honestly believe my problem is related to the first piece, which had white opal glass in it. The etched pattern on the piece in the picture practically mimics the white pattern of opal glass used on the first piece. It is as if the white opal glass weakens the kiln wash....or something like that!

I took your advice and used a diamond pad on each piece to remove whatever was there. They are back in the kiln for a fire polish, as we "speak" . I am hoping for the best turnout, but lesson learned...I won't use a kiln shelf more than once again without removing the old and apply a fresh wash.

Thanks again for the tips,
Connie

[Brock]

. . . And if I don't let the kilnwash dry at least a bit between coats, I just wind up dissolving the old kilnwash in the new...or making it too thick when they blend together. That doesn't happen for you?

Nope. I don't put on a specific number of coats, because after all the the slurry can change from mix to mix. I put on enough coats so that I can no longer see the color of the shelf, doing the usual alternate 90 degrees between coats. I normally pre-fire, (not if I am making magnets or small blanks) then use as required. Because of the base glass I normally use, I get anywhere from 6-10 firings. The effect on the bottom of the pictured piece is where that piece overlapped where a piece had been fired earlier. The KW is "stickier" where it has already had a piece fired on it. You can use this to your advantage. I once placed 121 magnets precisely on a shelf, fired and removed them then placed a large square piece on that shelf and fired it. That resulted in the back of the large piece having a pattern of squares on it, where the magnets had been. If you're going to use a shelf more than once, and you certainly can, just fire the large pieces first and work your way down to smaller pieces. You will not get any marks on the back that way. When doing this use the lowest possible temp/time to achieve your result.

[Valerie Adams]

1470° for a top temp in my kilns would be too hot for what you're doing. You didn't mention how long you held at that temp either. My top temp for a full-fused, two layer piece is 1440° with a 10-minute hold.

Your piece looks over fired to me, due to those sharp little points on the corners.

I routinely fire at least 4-5 times on a shelf before re-coating. And I also do all my coats at once, without letting them dry in between. I do stir my haik brush around with every dip.

[callidesigns]

Thanks to you nice people for your suggestions. I feel that I learned a little sumptin here and am glad that I got up my nerve and joined all of you fine artists. Here are pics of the coasters after coldworking with the diamond pads and a fire polish.