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

Wed Aug 20 12:36:30 EDT 2014

Thanks everyone. I will give ammonium chloride a try with somebody here at
UC Davis who has some experience applying/using it. I don't think it's a
generally applicable solution for photogrammetric reconstructions, but it
will be worth seeing if the software picks up the shape of the specimen
better after a coating is applied.

All best,
David

On Wed, Aug 20, 2014 at 7:06 AM, Janet Waddington <janetw at rom.on.ca> wrote:

> Aplogies if this went out more than once.  My webmail can be quirky.
>
>
> I agree with Roger, ammonium chloride sublimation can enhance surface
> details.  It takes some practice and skill to get an even coating,
> especially with larger objects. (That is an excellent video by the way)
> One caution - this is a sublimate, not a powder.  In humid conditions the
> resultant very fine coating will quickly dissolve leaving a fine invisible
> film of nitric acid on the surface of the object, which could be
> problematic. On a humid day it sometimes doesn't even make it to the object
> in solid form.  Just because you can't see it does not mean it has
> "vanished into thin air". It can also end up in the air of your storage
> cabinet if it subsequently evaporates off the object.
>
> I would worry about not removing it especially if the object is sensitive
> to acid. If the object is not sensitive to water, it can simply be rinsed
> with a fine stream or quick dunk into water.  I have used EtOH on specimens
> that do not like getting wet (e.g. shales) but don't know how effective
> that really is.
> Also, be aware that the black coating cannot be completely removed.  It is
> used to give a uniform background colour so any colouring is not a
> distraction, and to give contrast to the white coating. But if you plan to
> use your object for display it might not be as pretty afterwards.
> That said, sublimation is still a superb tool for studying surface detail
> and has been used for decades in palaeontology.
>
>
> Janet Waddington
> Departmental Associate
> Department of Natural History - Palaeobiology
> Royal Ontario Museum
>
> >>> "Burkhalter, Roger J."  08/20/14 9:11 AM >>>
> I will echo what Christian has said and add that ammonium chloride coating
> is relatively easy and inexpensive. It also works on a variety of 3D
> objects where the surface morphology is in need of enhancement. We have
> coated not only invertebrate fossils, but vertebrate fossils (especially
> teeth), and neontological collections including egg shells, herpetology
> scales, fish scales, and, as mentioned, archaeological lithic artifacts. A
> short video that includes ammonium chloride coating may be seen here:
> http://www.youtube.com/watch?v=g-FiFtBQthY&list=UUtNiqiI7zdCFS8QGiiYYRfw.
>
> Regards,
> Roger
>
> Roger J. Burkhalter
> Collections Manager, Invertebrate Paleontology
> Sam Noble Oklahoma Museum of Natural History
> University of Oklahoma
> Norman
> www.snomnh.ou.edu
> http://commonfossilsofoklahoma.snomnh.ou.edu/
>
>
> From: nhcoll-l-bounces at mailman.yale.edu [mailto:
> nhcoll-l-bounces at mailman.yale.edu] On Behalf Of Christian Baars
> Sent: Wednesday, August 20, 2014 3:21 AM
> To: 'nhcoll-l at mailman.yale.edu'
> Subject: Re: [Nhcoll-l] Dusting/powdering skeletal elements prior to
> photographing
>
> 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
>
>
>
>
> 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 > 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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-- 
David Katz
Doctoral Candidate
Department of Anthropology--Evolutionary Wing
University of California, Davis
Young Hall 204
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