[Nhcoll-l] Dusting/powdering skeletal elements prior to photographing

[Christian Baars]

David,

In palaeontology, invertebrate fossils are routinely dusted with ammonium chloride (NH4Cl) prior to photography to enhance contrast (often following blackening of the fossil), and in archaeology to eliminate reflection on shiny objects. The ammonium chloride is actually evaporated onto the specimen, which gives a very fine coating, much finer than you could achieve with any powder.

Ammonium chloride does not harm most types of objects and washes off easily with water, but will also evaporate from specimens/objects when left in a fume cupboard (no need for solvents in case of sensitive objects, just takes longer). Please let me know if you need guidance on the technique of applying ammonium chloride to the specimens.

I have had some very good results photographing fossils using polarizers. Commercially available polarizers can be very expensive; have a look on eBay for polarizing film which is very cheap, available in all sorts of sizes, and you can quickly and easily build your own purpose-made polarizer for any camera/microscope.

Kind regards
Christian



Christian Baars
Senior Preventive Conservator
National Museum Cardiff
Cathays Park
Cardiff CF10 4NP
029 2057 3302
christian.baars at museumwales.ac.uk<mailto:christian.baars at museumwales.ac.uk>




From: nhcoll-l-bounces at mailman.yale.edu [mailto:nhcoll-l-bounces at mailman.yale.edu] On Behalf Of David Katz
Sent: 19 August 2014 22:34
To: nhcoll-l at mailman.yale.edu
Subject: Re: [Nhcoll-l] Dusting/powdering skeletal elements prior to photographing

Rachel,

That is what I expected. I'm working on developing a developing a photogrammetry protocol for making digital models of skeletal elements. Photogrammetry does a good job capturing bone shape when the bones have texture or topography, or preferably both. However, some bones, particularly cylindrically shaped bones that have been treated so that they are smooth and shiny, really offer photogrammetry software no noticeable topography from which to find overlapping points between a set of photographs.

One option was to try coating the bones. It seemed to me this wouldn't be workable for the vast majority of collections. Francisco suggested a polarizer, and I will look into this. I hadn't heard of it before, but I've now found some reports that polarizers and photogrammetry software work fine together. The final possibility that shiny long bones shouldn't be modeled using photogrammetry software.

... We'll see.

On Tue, Aug 19, 2014 at 12:50 PM, David Katz <dckatz at ucdavis.edu<mailto:dckatz at ucdavis.edu>> wrote:
Hello,

I've been told that in order to photograph elements that tend to reflect light strongly (teeth, highly polished bones), people sometimes coat them with a reflection-reducing powder. I was even told that baby-powder is often used.

Realistically, what do natural history curators permit? Specifically, are there types of powder coating that are particularly acceptable and non-destructive? Are standards different for recent vs. ancient skeletal materials?

Thanks for you input.

David

--
David Katz
Doctoral Candidate
Department of Anthropology--Evolutionary Wing
University of California, Davis
Young Hall 204



--
David Katz
Doctoral Candidate
Department of Anthropology--Evolutionary Wing
University of California, Davis
Young Hall 204
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