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shrinkage and absorption of paperclay

updated tue 11 nov 97


LINDA BLOSSOM on sat 1 nov 97

Terry Lambert asked me about the absorption of paperclay. I decided to
send this to the list. First, the question, what is the clay body and
what modifications might have been made when paper was added. My clay body
has 20% fine grog. When I decided to try paperclay, I intended to decrease
and then eliminate the grog in my experiments. My clay had 10% shrinkage
with the high grog content. When I first added the paper, I increased my
fireclay and ball clay each by 10% (to make up for the missing percentage
of grog) and dropped my grog to 5%. My shrinkage went to 14%. Then I
dropped the flux from my clay, raised my fireclay and newman red by 10%
each and my shrinkage went back to 10-11%. I left my ball clay alone. In
this batch I did not add any grog.

In the original clay, without paper, the absorption was 6%. With the 5%
grog, increased ball clay and fireclay the absorption was still 6%. With
the dropped flux, increased fireclay and newman it was 5.4%

The other factor was the ratio between the soaked and boiled samples. This
ratio is supposed to be below .78% in order to be all right for outdoors in
the winter. In my original clay this was .75. With the increased ball
clay and fireclay with paper, it was .90. With the increased newman and
fireclay and dropped flux, it was .77.

I have made the paperclay by mixing the paper and adding the pulp to the
peter pugger and then adding the other ingredients. Then I tried what
Dannon said she had done. Just adding the paper to the wet clay
ingredients. It was a bit stressful for a while as I watched paper hanging
off the blades. I kept on mixing and pretty soon it was great. Lookes
like little cat hairs when you pull a piece of clay apart in the light. It
does get on the wire cutting tool. But I just made a large, slab built
cannister that was 17" in diameter and 17" high with this clay and it was
fine. Had all the structural strength wet that my high grog clay has. I
also made some tiles from 3/8" thick down to 1/8" thick and had not trouble
glazing them raw.

I found that a regular 2 1/2 gallon bucket full of shredded paper is about
the right amount for 100 pounds of clay.

Linda Blossom
2366 Slaterville Rd.
Ithaca, NY 14850

Cheryl L Litman on sun 2 nov 97


Earlier this year as I was just getting on Clayart, I remember vaguely a
discussion being ended about whether clay could stay out in the winter.
You've just mentioned that here again. Since I came in on that thread so
late, I never quite understood. Do you have time to elaborate on the
process of figuring out the ratio?

Cheryl Litman
Somerset, NJ

>The other factor was the ratio between the soaked and boiled samples.
>ratio is supposed to be below .78% in order to be all right for
>outdoors in
>the winter.

LINDA BLOSSOM on mon 10 nov 97


I think I didn't answer your question. I checked my sent box and didn't see
where I answered so here it is. First you get the absorption of the clay
by soaking it in water for 24 hours, drying it and then weighing it. This
tile should have been weighed immediately after coming out of the kiln so
that it had not atmospheric water. Subtract the dry weight from the wet
weight and divide the difference by the dry weight. Now boil that tile in
water for two hours. After two hours cool the water by adding some cold
water and dry and weigh immediately. Subtract dry weight from boiled
weight and divide the difference by dry. Now divide the first percent
(soaked percent) by the boiled percent and this ratio should be below .78
for the clay to be freeze thaw resistant. I hope that is clear.

Linda Blossom
2366 Slaterville Rd.
Ithaca, NY 14850