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slumping, humping, foam & other tid bits

updated fri 16 apr 99

 

rocky mann on thu 15 apr 99

Adding to the thread on using foam in slumping and humping: Aren=B9t you =
glad
that you=B9re a potter so you can use terms like slumping and humping=21

I have been using =B3foam=B2 for both slump and hump molds for over twenty =
five
years. The term =B3foam=B2 can be misleading because it can refer to a =
number of
different materials. What I have been using, and what I think most potters
use, is extruded polystyrene or EPS foam. Several companies make the same
material. The blue EPS is made by Dow and the pink is made by a company call
Formula R. Most building supply companies carry 1=B2 and 2=B2 thick EPS in =
2=B9x8=B9
or 4=B9x8=B9 sheets. EPS comes in two weight densities 150 and 250. I prefer=
the
250 density because it holds up better in a pottery studio and is better for
sanding. In my building supply store, 1=B2x4=B9x8=B9 250 densitiy EPS sells=
for
=249.12 a sheet, 2=B2 for =2418.24. Ask if your store has any damaged or =
broken
pieces. Sometimes they will just give them to you or, at the very least,
sell them cheap.

Although EPS can be cut with a utility knife or cut with a reciprocating
saw, I prefer to cut mine on a band saw because it makes a smoother cut. I
use a 3/8=B2 blade and tilt the table to a 45 degree angle. Next I sand all
edges and rough spots. Care should be taken here. Too hard a pressure with
the sandpaper can pull bits of foam out.

Although most of my slabs are humped, I slump platters on which I want to
add handles. After working the slab in place, I add handles and let the
piece get leather hard. I then place another piece of foam on top of the
platter. Spaces have been cut out of the foam to fit around the handles. I
flip the platter, smooth the bottom edges and flip it again, right side up,
onto another piece of foam. The lightness of the foam prevents the platter
from being crushed, bent or pushed out of shape. When It is stiff enough I
lift or slide the piece onto a board.

Humping onto foam is easier. I place precut wet clay slabs over the foam and
work it to fit the shape. On my pieces, the clay comes over the foam and
down onto the board to form a lip. In the leather hard stage I flip the
piece over onto a board and, because I am an impatient sort of guy, I use an
air compressor and shoot air between the foam and clay to separate the two.
The air compressor (one of my favorite tools) works well with plaster hump
molds too. I then bend the lips up a bit to shape them.

The boards I use in my studio are made of =B3bara board.=B2 This is a =
product
used as an underlayment on counter tops. It is dense, heavy and very smooth.
My building supply store sells a 3/4=B2x5=B9x8=B9 sheet for =2429.08. With =
care
these boards can last a life time. Some in my studio are over 25 years old.
Like wall board, it slightly absorbs moisture from the clay. Unlike wall
board, though, it can be used as shelving. When making tiles, I lay a slab
onto the bara board, cut the tiles with a knife and leave them untouched
until leather hard. I then flip them, smoothing the edges and leave them
until they are dry. I never get warping. There are variables of course: clay
body, relative humidity, and studio air flow to name a few.

Finally, I put the boards on ware racks. All my ware racks come from used
restaurant supply companies. I buy stainless steel racks with wheels with
room for 9 to 21 boards for =2475 to =24100. On the way home, I stop at a =
car
wash, spray the grim off and they are like new. Going to a used restaurant
supply company is like walking into potters heaven. Have you ever noticed
how bakers and potters use some of the same equipment and do similar things.
Besides racks, I have seen stainless bowls, trays, pans, baking equipment,
mixing machines, dough makers, rolling pins and much more all for bottom
dollar. In any urban area look in the yellow pages for used restaurant
equipment.

Old potters never die, they just turn leather hard.

-- Rocky Mann
Bar Harbor, ME
rockymann=40acadia.net