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Keeping things flat

#1 2012-11-07 16:53:19

kokopellime
Member
From: Washington, D.C.
Registered: 2012-10-04
Posts: 44

Keeping things flat

As part of my learning to work with PM as a medium, I took some placards of corrugated card stock (salvaged from shipping boxes), layered pulp over them and then applied some gesso.  I intend to use these placards for testing various surface treatments before applying them to my actual projects.  They'll eventually form a little library that I can refer too on how different techniques work (or don't).

At this point my work has been principally vessels (bowls, plates, vases) but I'm looking towards the future where I might do some sculptural forms, boxes, frames, mirrors and the like. This brings me to my question about PM and flat forms. 

After applying the PM (pulp), the placards tended to bend a bit upward due to shrinkage.  If I were creating a project that uses cardboard as an armature, how do you avoid such bending.

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#2 2012-11-07 18:47:45

Jackie
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From: England
Registered: 2002-09-14
Posts: 389
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Re: Keeping things flat

You obviously haven't read my book! (Papier Mâché Art &Design). I cover this topic in it. Not that this is a plug or anything! wink


Jackie

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#3 2012-11-07 20:22:06

CatPerson
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From: Washington State, U.S.A.
Registered: 2006-01-09
Posts: 1308

Re: Keeping things flat

The cardboard warps because glue/moisture is applied to one side and not the other side.

Hint:  "NOT THE OTHER SIDE."

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#4 2012-11-07 21:49:16

kokopellime
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From: Washington, D.C.
Registered: 2012-10-04
Posts: 44

Re: Keeping things flat

That makes sense - duh!

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#5 2012-11-08 02:58:45

kokopellime
Member
From: Washington, D.C.
Registered: 2012-10-04
Posts: 44

Re: Keeping things flat

Oops!  Jackie

I do have a copy of your book but I haven't read through it yet - my "bad".  I'm going to pull it up right now and do a bit of homework.

Thanx!

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#6 2012-11-08 04:41:35

CatPerson
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From: Washington State, U.S.A.
Registered: 2006-01-09
Posts: 1308

Re: Keeping things flat

Jackie has a lot of info in that book.

Sue

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#7 2012-11-08 04:43:27

kokopellime
Member
From: Washington, D.C.
Registered: 2012-10-04
Posts: 44

Re: Keeping things flat

Just checked out your book and saw your sage advice about using watered down PVA to coat both sides of cardboard.  I'll prep some additional card stock for my 'testing' placards over the weekend as you suggest.

You are such a fount of PM knowledge!

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#8 2012-11-08 10:15:56

Jackie
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From: England
Registered: 2002-09-14
Posts: 389
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Re: Keeping things flat

Thanks! If you use two sheets of corrugated cardboard, glued together in opposite directions, this will also help prevent warping - and make it stronger too!


Jackie

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#9 2012-11-08 21:37:05

bmaskmaker
Member
From: Takoma Park, MD
Registered: 2010-04-08
Posts: 93

Re: Keeping things flat

I've had differing levels of success with this.  Paper fibers seem to relax a bit when wet and tighten up when dry -- which can be a benefit (when doing something like a drum head) but is tricky when trying to create something intentionally flat. 

I've experimented more with this with strip mache (tho when doing something flat the 'strips' are full size sheets of paper) ... and have had less than stellar results.  The piece remained flat, but the part that was pressed against the foam didn't dry (not a huge surprise) ... and then when removed from the foam, when it dried the piece curled.

I have a paper-making book around here somewhere that shows an interesting mold set up where they were creating a mostly flat sun face with spires ... and didn't want it to warp when it dried. 

They layered wet paper sheets in the mold, and then placed hardware cloth over it (gridded wire), and had carriage bolts (or some kind of thick weighted nail) stuck through, and held up by the hardware cloth.  (Think the opposite of lying on a bed of nails.)  Each is holding down their small portion of the mold, so theoretically none should be inclined to warp ...

Nails (even carriage bolts) are made of strong but lightweight material now ... so I haven't found something comparable.  (Thought of gluing fishing weights or using lead weights shaped like nails ... but haven't moved on that.)

It's another potential option.   : )

-- b

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#10 2012-11-09 03:06:08

CatPerson
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From: Washington State, U.S.A.
Registered: 2006-01-09
Posts: 1308

Re: Keeping things flat

Flat PM items have always had problems with warping.  The human eye can see tiny imperfections in a flat surface, whereas on curved surfaces, the play of light on it can fool the eye more easily.

It took years and much experimentation in the 18th and early 19th centuries to find a way to keep flat pieces flat so they could be used for furniture.  They finally used steam to barely moisten the paper, and put it into heated metal molds that were clamped together.  They often didn't use any adhesive for this method, depending entirely on the dampness + clamping to fuse the fibers together.

The more water you add to the paper (strips or pulp), the more the paper fibers separate; and when the fibers dry, they tend to choose their own position (usually, where you didn't want) if they aren't forced into position by a mold.  To dry the PM, you have to allow for the moisture to leave the piece somehow.  If you have considerable moisture and the PM is clamped between two metal or solid wood pieces, that could take a long, long time.

If any of it stays in the paper, it may still warp as it finishes drying.  If it isn't completely dry and you use a acrylic-type adhesive (like PVA white glue), or any kind of impervious sealer (shellac, varnish, etc), moisture will be trapped inside, and you will get mold growing inside, which will eventually discolor the piece, even if painted.

Since steam and two-sided clamped metal molds are difficult to get hold of these days, the next-best way is to use a solid mold, and hold the PM against it with some sort of perforated material that will allow the moisture to escape.  Beth's description of the mold with hardware cloth bolted to it is a good description of this method.

Another method is to have two parts of the mold to trap the PM between, and one of the sides to have holes drilled into it to vent the moisture.  For instance, if you wanted to use a plastic bowl as your mold, you would need two of them, one intact, and the other with holes drilled all over it, and a method to keep them clamped together until the PM was dry.

When I have used the interior of a mold, I've filled pressed paper fiber with something like marbles, shifting them periodically, as I believe I've mentioned before.  The weight of the marbles presses the PM into the desired position, but the spaces between the marbles lets moisture escape.

The problem with all of these methods is that the clamping of the two pieces of the mold leaves a pattern on one side of the project.  If that side won't be visible, no problem.  Or you could sand the 'offensive' side.  Or you could add more PM to cover it.  Or you could disguise it with a surface treatment.

But if there's a simple, easy way, I've never found it.

Sue

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#11 2012-11-10 05:06:41

bmaskmaker
Member
From: Takoma Park, MD
Registered: 2010-04-08
Posts: 93

Re: Keeping things flat

Marbles!  Very cool.  And I didn't know that about the steam and clamped metal molds.  Sue, you are, as always, a font of great information.  : )

-- b

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#12 2012-11-10 22:31:04

CatPerson
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From: Washington State, U.S.A.
Registered: 2006-01-09
Posts: 1308

Re: Keeping things flat

Thank you, Beth!

A guy once called me 'a regular font of useless information'.  He wasn't what you would call a nice guy, but maybe he was just jealous that I knew that rats can't vomit, and he didn't.

Sue

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