hi julia,

what julianne said is right. the first thing I though of was: it'll go 
on fine, but coming off will definitely be damaging to a specimen like 
that. the reason why illustration is so important to the field of 
paleontology is precisely because the common discoloration of fossil 
specimens does not read well in life; more so in photographs. the artist 
takes on the challenge of depicting the form is space while eliminating 
local coloration and visual noise of breakage. the process definitely 
takes time and focus. occasionally you get lucky and the preservation is 
good. in rare cases of badly discolored, robust material (and with full 
knowledge and permission of the curator) we have used the burning of 
magnesium strips to coat a specimen with white smoke that rises up from 
the metal. the powder, like that from ammonium chloride, can be brushed 
off little effort. with a specimen like what you describe, even the 
tiniest, softest brush will be too aggressive for the fragile bone. to 
compound the matter, the coating will serve to mask the bone during 
brushing and hide the damage-in-progress. proceed with caution.

good luck!

-frank

> STOP! STOP! STOP! Do not do apply any coating of any sort to the 
> fossil. It is already fragile and the surface is flaking off by just 
> touching the "cotton pad". Applying anything to the surface will, 
> especially anything abrasive, and then trying to brush it back off 
> will destroy what is left of the surface. The specimen is obviously 
> friable now. Please don't make is worse. I say this as a former 
> vertebrate fossil preparator and geology collections manager charged 
> with maintaining rare and fragile specimens that have great scientific 
> value. I have seen way too many fossil destroyed by mishandling.
>
> As a preparator, I consolidated, repaired, and reconstructed many 
> fossils. It is a delicate business akin to conserving a work of art. 
> The wrong material or preparation technique can render a specimen 
> worthless for scientific research. I have to admit, I am surprised 
> such a fragile specimen was sent out on loan.
>
> All that said, I wish I could give you tips on how to better see the 
> surface shading. Unfortunately, there is no simple solution. You might 
> try a strong, raking light but please to not apply anything to the 
> surface of the specimens. And, Britt is correct, the curator's 
> permission (in writing, detailing exactly what he/she is allowing you 
> to do) is critical if you do intend to treat the fossil.
>
> Julianne
>
> Morgan-Scott wrote:
>> Hello,
>> I have a question about fossil photography -- I have been working on 
>> a series of drawings of a small prehistoric mammal, Neocnus, from an 
>> on-loan specimen which is very fragile.  This fossil drops flakes 
>> every time it touches the cotton pad it's sitting on.
>>
>> We photographed it and I have been using the photos for initial 
>> drawing set-up.  However, eyeballing the fossil to get the shading is 
>> very difficult because of the coloration:  the outside of the fossil 
>> is blackish, and the broken areas, of which there are many, are 
>> almost white.  It's confusing to the eye and makes it take longer to 
>> complete the drawing.
>>
>> I know that fossils can be coated with ammonium chloride for 
>> whitening, and I've read articles which detail the techniques 
>> (vaporizing the ammonium chloride and airbrushing with powders) for 
>> applying it.  The directions seem unnecessarily complicated to me but 
>> I've never watched anyone do it. The directions for airbrushing say 
>> to use "Bon Ami" scouring powder in alcohol! Why not titanium dioxide 
>> or even a bit of talc?
>>
>> Directions for removing coating simply say that "it easily brushes 
>> off." How easily?  Any help would be appreciated!
>>
>> Thanks, Julia Morgan Scott
>> Need to leave or subscribe to the Sciart-L listserv? Follow the 
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>>
>>
>


-- 
Frank Ippolito
Principal Scientific Assistant
Division of Vertebrate Paleontology
American Museum of Natural History
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