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Monday, 5 March 2012

Simulating a fossil, part 4

Now comes the actual casting of the simulated fossils.

For this, you need cement, water, spatulas and some patience.  You also need newspaper spread out to work on.  Use plenty of paper, so that any spill of wet cement can be absorbed before it soaks through.

The first thing to do is to wash the plaster very thoroughly and then soak it in water for 24 hours, to get rid of any residual acid. This may or may not be necessary, but cement reacts with acid, so I rinse everything, just to play safe.

Then I add some water, not a lot, and start adding dry cement powder. Anybody who has mixed cement will know that this is wrong: you should always add water to cement, but the aim here is to get the cement right down into the crevices. I got some better shots of the second one, so now we will switch to that:

I keep adding cement powder until it is a stiff paste, and I use the spatula to keep pushing the cement down against the plaster.  If the gets TOO stiff, I add some more water.

Banging the tub to bounce the bubbles out.
 Then I pick up the container and bang it a few times on the newspaper that I laid down at the start. This makes the cement more liquid, and bounces out most (or all) of the bubbles in it.

Now all I have to do is leave it aside for a few days.  When I was doing another set of shots for Australian Backyard Naturalist,* the book this was intended to go in, one of the cement slabs broke up under the work I was doing on it—work which will be described in the next blog entry.

That was rather vexing.  I tried slipping a piece of plastic flywire into the next one that I made, and that one didn't break up.

Maybe I was more careful, but this may be worth trying.

Anyhow, after that, you just have to wait a few days, before you can tip out products like those shown in the last picture.

This began with Part 1; (which is the best place to start!)

It continued in Part 2;

And then in Part 3;

It has now been finished in part 5.

*  For those who came in late, the book referred to above is due for release in May.  It is written for ages 10 to 14, and for that reason, we decided to leave out stuff like acids which I was certainly playing with when I was 11, but these days we are a bit more safety conscious!

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