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Tuesday, 6 March 2012

Simulating a fossil. part 5 and final

 OK, all good things come to an end.  I have been outside finishing off the exercise and photographing it.

But before I start explaining the finish, there is one thing you need to do when the cement has set for two days.

At that time, it is still soft and crumbly (which is good) and it is inclined to break (which is bad).

So be careful, or leave this step out. I decided to use my "fossils" as paperweights, so I wanted a base that was rough, so I could glue felt, but even, so it would sit flat.

That meant grinding the base on a masonry block that I happened to have handy. A brick would be just as good, but it makes a mess if you use a wall or a path.  Young readers in particular, BE CAREFUL!!

Just work the blocks, one at a time, in a circular pattern, and you will get the sort of surface you want.

Then it is time to set the blocks aside and be patient.

I actually wrapped mine up in the newspaper you can see in the fourth shot, and damped it down.

Cement that is kept damp sets much harder, I was always told.

Jumping ahead, this is what we get to by the end of this blog entry, but there are a few tricks that you need to apply along the way.

It occurred to me, as I was working, that I needed a shot of the set-up and tools.

First, plaster is going to fly off in all directions and make a mess, so I work in a tub.

Second, the cement is fragile, so I need padding under it, in the form of newspaper.

Third, while I am hammering probes and chisels into the plaster, this has to be done very gently: you tap, rather than bash.

Also, it's a good idea to take small bits, not large ones, and never drill into it, because like a real fossil hunter, you don't know exactly what is in the matrix.

A moral tale here: I am an enthusiastic amateur, but I sometimes help the pros, when they need extra warm bodies, so I know what to do.  In 1986, I was involved when an area in a quarry at Somersby, north of Sydney, was held for a limited time for diggers to extract as much as they could.

I set up a promising-looking area, cleaned away the detritus and put my tools down to have lunch.  Bad mistake, almost a disastrous mistake, because an idiot gardening writer from Canberra came wandering along, saw what others were doing, and started bashing into my carefully-prepared site, flipped a slab over, and went to smash on down though the rock.  Luckily, a pro saw the underside of the slab as it flipped and stopped her.

When you work in shale, the fossils occur between strata, and while you lose the top half as you clear a layer, the lower half can be preserved and taken out whole.  That's the deal when time is limited.  Anyhow, this moron was about to carve through the lower half, but she was stopped, just in time.  It was the rarest find of the whole dig, and I heard from others that she was still dining out, years later on her brilliant find!  Grrrr!!!  Be gentle, go slowly!

Volunteers cleaned this Devonian fish slab from Canowindra, using toothbrushes
and wheat-bag needles (those are like sailmakers' needles, but even bigger.)
These are the principles that I am applying in this simulation.
Here, we are simulating the situation you have, for example, when you are extracting corals from limestone, or fish from a slab. The simulation is easier than the real thing, and you can do in an hour or two what would take a week in real time, but the methods are the same.

There are really just two rules: 

* be gentle and slow; and

* always work towards the outside.

The main tool that I use here is a carefully-blunted 6" nail (150 mm nail if you like, but it came from a jar of nails bought in the 1970s, so I bought it as a six-inch nail).

The other tool I use is an old dissecting probe: you can see it in the equipment shot above and in the next picture.

By the way, special safety rule: think about where the probe will go if it slips.

Be careful!

Now the next stage is to get rid of the plaster, and for that, I used a scrubbing brush. Normally, I save old tooth brushes for jobs like this but some Tidy Person in this house seems to have deep-sixed them (either that, or I have used my entire stock!)

And now you can see how I simulated some fossil shells. All that is left is for me to let them dry, glue some felt on the base, trim the felt—and maybe add a coat of clear lacquer.  I will experiment with one of the broken ones.

If I were doing this in a class, I would now ask my audience to research fossilisation, and prepare a list of the ways in which this is a reliable simulation, and in what ways it is unreliable. I would never do that here, but feel free to comment!

This is the last of a series of five pieces. If you landed here, I suggest that you go back to part 1, read that, and follow the links through to each of the other parts.

As for me, it's about time I got some work done.  Catch you in a week or so.

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