Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[jasperb]

Hello everyone, I have found lots of helpful information on this forum regarding stabilizing of various materials but I haven't found any information on my questions below.  However, in case I missed them, please do point me in the right direction!

1. I have several large pieces of dinosaur bone (weighing several pounds) that I would like to cut.  However, several of the pieces have pretty pronounced fractures and a couple of other ones are rather "crumbly".  I tried cutting one piece and, although the end cut did stay intact, i am concerned that subsequent slabs will likely fall apart.  I have read a lot on this forum about stabilizing slabs with HXTAL or other epoxies, but I haven't been able to find any information yet on stabilizing large pieces before they're being cut.  If possible, I would like to stabilize these pieces prior to sawing them to minimize the risk of them falling apart.  Does anyone have any recommendations regarding best process, required equipment, and epoxy to use?  I am willing to invest in a vacuum unit and whatever else may be required.
2. Assuming that a vacuum unit is required to address my first question (and assuming that the piece to be stabilized would be submersed in the epoxy during this process), is there a way to avoid epoxy from curing on the outside of the piece?  Several of these pieces show great bone structure on the outside, and I'd like to keep them "natural" if possible.  I have considered using paraffin wax to mask the outside areas I'd like to protect (i.e. cover select areas of the outside with wax prior to submersing in the vacuum chamber), as well as air abrading any left-over epoxy after it has cured.  Any recommendations on this?

Many thanks for any and all advice.  I have cut and polished a lot of thundereggs, but am new to working with larger pieces of dinosaur bone.

Jasper
 

[irockhound]

I have taken a Dino bone roughly 8 inches tall and 3 or more inches thick with a diagonal fracture running thru it.  I used Hxtal and just made tape and plasticine clay dams to keep the sealer from leaking out the sides of the fracture.  After curing I sawed the bone with zero problem and the fracture held perfectly while sawing.  I love Hxtal for sealing large fractures.  I just use the kids plasticine clay from Michaels to make the dams.  Just a note that I am sure you saw from reading the posts I used a 100 watt old style incandescent bulb to warm the bone and hxtal allowing the sealer to thin and penetrate deeper before curing.  I do not use a vacuum and the thinning from heat normally penetrates all the way thru but depends on the fracture.  I have found Dino bone fractures are much more porous unlike say a fracture in a slab of montana agate where the vacuum might be necessary.  You can always also fill from one side cure flip it and cure from the other side too.

Just a side note I wait about a week to make sure everything has reached a full cure, probably way longer than needed but I side with caution.

Steve

[jasperb]

Steve, thanks very much for the advice - exactly what I was looking for.  Several of the pieces that I'd like to cut are close to 8 inches thick, so I'll likely try my luck with a vacuum chamber (it will come in handy for mineral prep work anyways - my other passion) to increase the odds of stabilizing the entire piece, and also follow up your recommendation of treating the piece on both ends.  Many thanks!

[R.U. Sirius]

Steve makes an important point about the heat temporarily "thinning" the resin. Heat-cured epoxies in fact go through a brief drop in viscosity just before cross-linking reaction starts turning them into the solid.

Depending on the design of the vacuum unit, you might be able to pump the chamber down, thus evacuating air from any open pores in your material, and only then flood the piece with epoxy mixture and break the vacuum to force the epoxy inside the pore space. This is preferable over cheaper systems where you first immerse the sample, and then apply vacuum, causing foaming.

You could get the impregnated piece out and wipe the surface with lint-free fabric, then heat-cure it. It's a messy business!

Keep in mind that the centre of your 8-inch piece might take several hours to reach the prescribed cure temperature - and this is in a proper oven. I don't think using a light bulb will work properly for such large pieces.

One last thought - since penetration of the resin and ultimately the stength of stabilized piece depends on a lot of factors (porosity, viscosity of the resin, size and shape of the material, timing of your steps, vacuum pressure) some experimentation will be needed. If the epoxy you are using is fluorescent, you could slab the stabilized piece and then look with UV lamp to determine if penetration was full or only superficial.

[jasperb]

Thanks for the additional recommendations.  I am only familiar with vacuum units in which you immerse the piece (or alternatively apply the epoxy mixture to the surface on which the fractures are exposed) before pumping the chamber down.  Could you point me in the direction of a unit that enables you to first create a vacuum and only then apply the epoxy?

I am planning on using HXTAL, so I guess heat curing won't be required - just patience and time?

Many thanks

[R.U. Sirius]

Here are examples of units that allow for pumpdown prior to dispensing/immersion:

https://www.buehler.com/cast-n-vac-1000-vacuum-system.php

https://www.struers.com/en/Products/Mounting/Mounting-equipment/CitoVac#

Might not work for the sizes you are interested in, but these at least give you some idea on the mechanics. You might be able to improvise.

EDIT: just to add - if you download the technical data sheet for the Struers unit above, you will see that it can fit pieces of up to 20cm in diameter (almost 8 inches).

[jasperb]

Thanks - very interesting, I hadn't seen this type of vacuum chamber before.  It looks like this could work well if a piece needs to be completely submersed in epoxy.  Probably more difficult to work with if you want to apply epoxy to discrete areas only, and not the entire piece.  Thanks again!