Kiln wash 'crawling' on shelf.

[Buttercup]

Recently I purchased a small used kiln, made in 1979. It looks new, the interior is pristine, max temp 1100 º C. It came with three shelves, 12"x12". They look like ceramic paving stones with an exceptionally smooth upper surface. Two were wrapped in a 1980 newspaper. On the underside is 'ACME' in a small circle. The nearest reference I can find on-line is Acme Marls, who seem to be out of business, but there is no information about the composition of the shelves.

The person I bought it from knew nothing about the kiln etc. as it had been his mother's who bought it to paint and fire porcelain.

The unwrapped kiln shelf accepted several layers of kiln wash. On the others the KW 'crawled' leaving clear shiny patches.

1. Does this mean that one shelf has been used and fired and I can safely use it?
2. What are they likely to be made from?
3. How can I treat the surface of the other two so that they will accept KW?
4. Do I have to pre-fire them as they don't look as though they have been used yet?
5. Sometimes I like to fire on whiting, (Albin's method). Do these shelves still need to be KW'd if whiting is used? I want to be able to KW them anyway, for projects other than painting.

The kiln will soon be connected to the GB4 controller and I'd sincerely appreciate any information that will help me get the shelves into use. Jen

[Kevin Midgley]

Prefire.
I would not use regular shelves for staining.
Use metal trays filled with whiting that can be dumped out after each firing of stain face down on the whiting.

[Buttercup]

Thanks Kevin. I do use a shallow stainless steel tray with whiting for painting and staining. I have personal experience with silver stain accidently transferring from a kiln shelf to the back of a piece of painted and fired glass I made during Albin's course at Pilchuck. He put contact paper on the front and washed the back with diluted hydrofluoric acid. It came off.

Do you have any idea what the ACME shelves might be made of? They look like fine, smooth stoneware, a light tan colour.

To what temperature should I pre-fire them....just higher than I intend to go?
Thanks again,Jen

[Stephen Richard]

............
1. Does this mean that one shelf has been used and fired and I can safely use it?
Who knows? but you can fire them, which might make them accept kiln wash more easily. Usually the place where the kiln wash appears to lack adhesion is a more dense part of the shelf.
2. What are they likely to be made from?
Something that is high firing, since porcelain takes a higher temperature than painting or fusing
3. How can I treat the surface of the other two so that they will accept KW?
Try firing to ca. 800C. I have found that usually there is kiln wash even on those "clears areas", just not as much.
4. Do I have to pre-fire them as they don't look as though they have been used yet?
Wouldn't hurt.
5. Sometimes I like to fire on whiting, (Albin's method). Do these shelves still need to be KW'd if whiting is used?
Not in my opinion.
I want to be able to KW them anyway, for projects other than painting.
.....

[Buttercup]

............
1. Does this mean that one shelf has been used and fired and I can safely use it?
Who knows? but you can fire them, which might make them accept kiln wash more easily. Usually the place where the kiln wash appears to lack adhesion is a more dense part of the shelf.
Thank you Stephen.
Today I checked the shelves I'd KW'd yesterday and there's a large circular area in the middle of the shelf that appeared to have taken the KW the best.It looks like a patch of oil.
2. What are they likely to be made from?
Something that is high firing, since porcelain takes a higher temperature than painting or fusing
3. How can I treat the surface of the other two so that they will accept KW?
Try firing to ca. 800C. I have found that usually there is kiln wash even on those "clears areas", just not as much.
4. Do I have to pre-fire them as they don't look as though they have been used yet?
Wouldn't hurt.
5. Sometimes I like to fire on whiting, (Albin's method). Do these shelves still need to be KW'd if whiting is used?
Not in my opinion.
Thank you very much Stephen.
I want to be able to KW them anyway, for projects other than painting.
.....

Can I safely fire them to 800 C without KW totally covering them, or should I sand off what is on them?
Thank you so much for that information, Stephen.

Does anyone recognize the ACME branding on the underside of the shelves and know what they may be made of?

Look forward to any further clarification. Thank you, Jen

[Valerie Adams]

Looks to me like they should be durable shelves:
http://fortpottery.com/webpages/KilnSup ... lving.html

[Buttercup]

Thank you Valerie. I found this link when I was looking for information but it didn't show the 12" x 12" shelves that I have so I am not sure if they are the same type. Even so, I'm still not sure how to prepare them. Today when I looked at the shelf I thought had been successfully KW'd it had a round stain, like an oil mark, covering most of the shelf.

If the stain is oil-based, can I safely fire the shelves to 800C, as suggested by Stephen, without a KW coating evenly applied?

To date I've painted and fired on whiting on a stainless steel tray and have no experience with KW other than on moulds for draping.

I'd really like to know how I can get these shelves to accept KW, without it crawling and leaving exposed areas.

Thanks so much for the input.
Jen

[Valerie Adams]

If these shelves don't hold up to an initial firing (which I can't see why they won't), they'll be wasted anyway, so why not just fire them and see?

One of my smaller kilns is a funky size so I buy old pizza stones whenever I see them at garage sales. They're usually covered in grease stains but I just fire them to about 1500° and they come out nice and clean.

[Bert Weiss]

Valerie, I once toured a kilnshelf/furniture factory and sitting next to the stacks of shelves in the factory were the stacks of pizza stones. They were identical. The good news for us is that at 1500°F our kilns are "self cleaning".

The worst case scenario with the smooth shelves is that they are glazed tiles. If so, they will be resistant to kilnwash and they will stick to glass. If they are just really smooth porcelain, you could try and rough them up. I suppose the worst case is that they are prone to heat shock and could crack, but that is not necessarily the case.

A rule of thumb for how hot to prefire is 50°F hotter than you plan to use them.

[Buttercup]

Thanks, Valerie. That makes so much sense.

Thanks,too, Bert. The kiln is rated to 1100ºC so there's plenty of room to fire higher than I'll ever need. Hope to use it to make some moulds, too. Jen