You will probably get all sorts of ideas for this.  It depends on what your drying conditions are.  I have done some similar stuff (large fish etc) by creating a shape in damp sand, covering it in clingfilm or foil,
then one of two approaches - laying pieces of cardboard over (small enough to follow the curvature), taping them before gluing on a second layer of cardboard and then laminating with paper
or - creating a layer of Modroc (plaster of paris bandage) before laminating with layers of heavy paper and using a strong paste.
If you use the Modroc method, you could use this layer as your mold for making the repetitive pieces.

What about doing what you're doing, and then gluing the newspaper PM to a piece of cardboard that is cut the same shape?  The cardboard should add strength and the PM would make the design.

Are you going to keep them flat, or curve them to fit the boys?  I'm not trying to complicate things, just wondering.

To accelerate the drying, put them in front of a fan.  Even if they're lying flat, the air moving across the top will help.

Sue

I'm with Jackie on this one, I think.  I'd start with a cardboard oval or circle as my base.  Perhaps take a slice out of it on either end and tape it together to make it curve a little, if that's what you want.  Then paper mache it to get strong ... then add the shell details with more cut out cardboard shapes, strip paper mache'd on. 

For strong paper mache, and to build up layers quickly, I laminate multiple layers of pasted papers on a flat surface first, layered in opposing directions (which helps add strength).  It lets you build up 6-9 layers fairly quickly, then let the whole thing dry.   You can alternate brown paper and recycled office copy or bond paper, each offers different properties and it's easier to tell how many layers you've built up and where you've left off. 

I also add a bit of plaster to my paste mixture (a tablespoon to a pint of paste) when I want to add an additional level of strength. 

Sounds like a great project. 

Another option for a form, might be to use a trash can lid as the base.  You can make a paper mache copy, or if you're in a hurry, wrap plastic wrap around it, then use packing tape (clear or paper) to cover it, in opposing directions in 3 layers.  You can then cut this off your form, because of the plastic wrap, and tape it back together where you cut it ...  The tape should let it hold its form enough for you to mache it to strengthen.

Then when the form is strong enough, cut turtle shell sections out of cardboard and build up your shell detail that way. 

Sounds fun.

-- b

When I make turtle shells, I usually create the basic shape first, and then glue the raised elements/border on top of that, which is pretty much what the others have already described.  My shells are always part of a figure though, and usually miniatures at that, not stand alone pieces meant to be worn by humans.  Here's an example of a Teenage Mutant Ninja Turtles Mecaturtle 2.9 cm (1.1") tall figure that I made using that technique:



The tray you're using certainly provides an appropriate turtle shell surface texture, although real turtle shells tend to be oblong, rather than a perfect circle.

If you're really concerned about strength, putting some wire inside the shell, perhaps around the circumference, might help as well.  But cardboard, and several layers of paper, as others have suggested, should be strong enough, provided the boys aren't planning on using them to stand on or something similar that would subject them to considerable structural stress.

Last edited by Patraw (2013-02-11 16:25:58)