My First Dig/plaster! (Kangaroo Limb)

[Ash]

Hey guys. This is the first bone I've had to properly dig out and use plaster on. A few Q's and some Pics.

What's the plaster of Paris/water mix ratio? And do you use glad wrap or alfoil over the bones? I've heard both. If alfoil, how do you get it to stick around tight over the bone? It seems to just lift off and not cling/conform to shape. Still have to dig around the back of it and form the pedestal for removing it. Will do that this weekend hopefully. Pics show from finding it to where I'm at now. Is a Pleistocene ages kangaroo limb bone I think.

[tooth_claw]

Congrats!

Plaster should be added to water until the water cannot soak up any more, then mixed. you will want a thick, custardy sort of consistency (don't muck about too much as time is a factor). The actual amounts and ratios are something that you need to learn by doing it, the weather and water quality can affect the mix (don't stress too much- it is pretty easy to tell if your mix is too thick or thin).

If you can, consolidate the specimen (Paraloid!) before excavating it too much, that specimen is in a lot of bits already and you need it to remain stable so that you can actually move it.

Then dig around the specimen (about 2cm from the bone) and pedestal it.

Usually, I would use a brush dipped in water and stipple a couple of layers of toilet paper over the specimen to provide a recognisable layer on the exposed surface (resist the urge to expose too much!) and then pack it with about 5 cm of damp sand. Then plaster/hessian over the sand. This will give a wide margin when you are cutting the plaster off.

Let the plaster dry and then carefully excavate underneath the specimen-leave plenty of dirt under it (at least 5 cm-probably more) so that the bone does not fall out of the plaster jacket.

Then hold your breath, pray a bit and gently roll the specimen in one smooth movement onto the plaster lid. This is where you can lose the specimen so be prepared!

Gently remove the dirt from the bones' underside but don't take too much away-that can be done in the lab!

Repeat the toilet paper/sand plaster method so that you have a sealed capsule to take home.

This careful method has never failed me yet- even on the biggest, most fragile bones.

Good luck!

[Ash]

Thank you so much! I shall rise early Saterday and get back to it. Been using a dentist pick to remove all the sand, so going fairly steady.

Paraloid - where can I get this, is it a brand, or any brands in particular to go for? Lightly brushed on?

Thanks for your mega-detailed response.

This may be a rib? More work will tell!

What have you excavated, if you don't mind me asking? Your display picture says we may have a common interest.

[Vordigern]

great find! Congrats and good luck

[tooth_claw]

You can buy Paraliod from our good friend Dr G at digitup.com.au.

Google 'Paraliod B72 Amy Davidson' and follow the www.academia.com link to get a paper detailing the use of the product.

It is awesome, I use it all the time to prepare and consolidate fossils.

Like this one....(Diprotodon optatum skeleton).

[Ash]

My Gosh! One day i hope to "merely" find the skull of a diprot, let alone associated bones. Which state are you in? I'm SE QLD. And where have you been hiding on this forum

Yeah, i know Dr G. He helped with the ID of my P. goliah jaws (we weren't sure what Procoptodon species it was).

[RichW9090]

I'll add a few comments here.

First, excavating to a couple of centimeters from the bone is way too close. Always take much more matrix. I would go at lest 4 and perhaps 6 inches away from the bone, no closer. It is far easier, and far better for the bone, to do the real exposing of the bone in the lab, rather than in the field.

Use lots of TP, stipling it on with a wet brush. Layer upon layer, at least 1/8 inch total thickness, and better 1/4. Use the wet brush to gently "jab" the paper into all the cracks and crevices, filling them so that no plaster gets wedged there, or in undercuts. Do not add sand or loose matrix on top of the paper. Plaster bandages go directly on the paper.

Always use a strengthening agent like burlap strips, or for rather small specimens, gauze strips. Some of the medical supply houses carry plaster bandages for making casts for broken bones. Make sure you get the ones with actual plaster, and not the new plastic compound bandages. These are good for small fossils.

Never use aluminum foil, as it prevents the matrix and the specimen from slowly drying out.

Mixing plaster is messy business, and I'm convinced that the only way to do it is to get both hands up to the wrists into the plaster.

Let the plaster dry until it is cold and completely set. Probably the most common mistake I see is turning the jacket over too quickly. The second most common mistake is having over-exposed the bone before jacketing. Some people just can't resist see as much of the fossil in the field as they can, and it invariably costs the greatly in the quality of the finished specimen.

Add something as a stiffening brace to the jacket if it is a large one, or a long narrow one like yours, so it won't twist or break in the middle.

Always flip the jacket and put a plaster cap on it. Resist the urge to take small jackets home without a top - you'll eventually lose a good fossil that way.

Yes, I over-jacket my fossils. In 45 years in the business, I have never, ever, lost a jacket in the field. Most of my colleagues lose jackets all the time - the matrix falls out when they flip the jacket, or the jacket collapses or breaks in the middle when they go to lift it.

My comments are directly primarily at Neogene fossils. Paleogene fossils, or dinosaur fossils, are a bit different and take different treatment.

Rich

[Ramo]

Here are a sequence of photos I took last year, while teaching my little brother to jacket in the chalk. It is a little different than what you are doing, as we usually want the plaster to contact the bone, and the layers of chalk usually split easily below the specimen, so not much undercutting is required (usually). This was just a fish tail, and we were in a hurry, and we didn't get the plaster mixed as good as it should have been. It was a little lumpy, but it turned out fine. We got the entire (actually partial) tail out successfully. I know this is a day late, and a dollar short, but I thought someone might find this useful.

Ramo

[jpc]

Hi Ash... congrats in a plasterable find. It is a lot of fun, but messy. Lots of good advice from the other folks. I would agree with Rich, that 2 cm is not enough. Take more if you can. I, on the other hand, use aluminum foil and rarely put a cover on the backside of my jackets. I carry them home upside down and it works. They dry out and then I clean the bones usually form the bottom side.

[tooth_claw]

All good advice and well worth paying attention to! I have to agree with RichW9090, be as cautious as possible and take the matrix if you can-my 2cm radius is a bit on the skinny side (developed to shed kilos from a large cast so that we can actually move it), you can always shed the matrix later and you never know what lies directly below...

[Ash]

Just had a crazily hard amount of rain. I did rebury the fossil, but i dont hold high hopes. Will find out friday.

Everyone: Thanks for all the tips and advice. I'll be buying a bag of plaster friday, did get some hessian bags today though.

Fingers crossed!

Gotta hate finding things on a sunday afternoon and running out of daylight, with work for the next 5 days..

Cheers,

Ash