8 replies to this topic

[Megaselachus13]

Sometimes I've observed at some shark teeth specimens where the prolonged exposure to the sun, produced that the exposed areas of the enamel are degraded by dehydration.
In these cases the specimens show a whitish and lacking in brightness aspect at those degraded areas.
How in nearly all, there are degrees of degradation of the enamel depending on the time and intensity of direct sunlight exposure. I guess it also depends on the color of the enamel, the darker tones are dehydrated before the soft tone ones.
Is there the possibility to re-hydrate these areas or artificially restore the natural color of the specimen (without using dyes or watercolors)?.
Sorry my bad English, hopefully you can understand what I mean.
Best regards and thanks for your attention.

[tracer]

color removed by exposure to uv radiation is gone, so if you want color back, you'd have to artificially add it. any decalcification/leaching caused by exposure also isn't "reversible", so if you want shiny and smooth, you'd have to add something to render that condition, such as vinac, butvar, or some other copolymer or substance of choice.

enamel, and i assume enameloid, has a very low water content to start with, so i don't feel that changes in it's color and state of preservation is due to "dehydration" per se or that water can be added to it and change anything.

[Wakaritai]

Well, that covers UV exposure, but not dehydration. So, whether or not that applies depends on the actual cause of the discoloration (sun exposure, or dehydration).

That being said... I don't know what, if anything, can be done for dehydration. If anyone has any (safe?) rehydration techniques, I would also love to learn. Some of my best-preserved ballerphon graphicus specimens have been in dark but dry conditions, and the "shells" have gradually been changing from clear to an opaque white color. I've considered trying to rehydrate them, but I haven't tried anything yet as I've been worried about ###### up the fossils. My main concern is the threat of stress fractures. Again, I don't know if there is actually any danger of stress fractures, but I haven't been brave enough to take a chance.

[tracer]

dark but dry conditions where? and how did you determine that dehydration has something to do with the change in the specimens?

have you established that it could not have been something else, like bynesian decay?

link

[Paleoc]

I had to chuckle at this topic.
This is one of the first Bone Valley teeth (Hemipristis) I ever found. When the tooth is dry, it is virtually all white in color. When you wet the tooth and let the water soak in, the blade turns light blue. It then drys back to white. It actually turns slightly darker blue than the picture but it drys very fast so it's hard to get a good shot.

Edited by Paleoc, 09 September 2010 - 05:00 AM.

[tracer]

it's a technical point, but i don't think the tooth is "turning blue". i would think the blue simply shows better through the surface when the surface is perfectly smoothed out by the water. you can see the phenomenon with almost any rock that has lots of microscopic surface scratches. the rock looks whitish, drab, and not worth picking up, but then you wet it, and suddenly it's gorgeous. but these rocks are not "dehydrated", because they didn't have water in them to start with. it is the thin layer of water on top of and at the surface of the rock that fills in and eliminates the light being refracted 87 million different ways by all the scratches, efflorescences, dings, patinas, oxidations, and other non-clear, non-pretty surface features.

don't get me wrong - there are of course some hydrated rocks, like opal, for instance. but my point is that you can achieve the same effect on many rocks by finely polishing them as you can by wetting them, so it isn't a water issue.

if you want to experiment with a somewhat removable "glossing" agent, you could try vinac in acetone.

[Megaselachus13]

I know that it's very difficult to rehydrate a fossil definitively (other than that it's permanently submerged in water).
However in those specimens less hit by the solar action is still possible to make them look partially wet and partly return them the original color.
This can be achieved with water, olive oil, paraffin oil, animal fats and suppose that a host of other possibilities. However the effect isn't deffinitive and it's duration will depend on the degree of evaporation of each of them, leaving some of them residues once evaporated.
There are cases where the fossils are dehydrated because even cleaning methods such as echinoids whose treatment with KOH, sometimes leaving a powdery and cracked appearance when the specimen dry.
This can be solved by impregnating or bathing specimens in any of the aforementioned substances to give them a moist appearance (hidding those deffects from potash). But this is too a temporary remedy.
In the case of shark teeth, I don't know the amount of water that they may have in their composition but there are abundant specimens that exhibit dehydration cracks in the enamel or the root (or both).
Furthermore it's clear that this phenomenon is more obvious or exagerated at the specimens of greater dimensions.
Having say all this, what do I know whether it's very helpful regarding the original question...I ask again if there is a final product that still partly recover the original tone definitely.
Perhaps there are products used at natural stone works (like granites, marmors, etc) or with artificial products like Silestone, Compaq and others to give a finish that enhances the brightness and the original color definitely...But I don't know about theese kind of products or if they exist.
Thanks for your interest and responses. Please, forgive my insistence but I think it's a interesting question.
Greetings.

[tracer]

I have been under the impression that the characteristic cracks in fossil shark teeth were hydration cracks caused by expansion/swelling in the fossil from environmental moisture, as opposed to dehydration of the original native moisture from the teeth.

[Wakaritai]

tracer, on 08 September 2010 - 08:12 PM, said:

dark but dry conditions where? and how did you determine that dehydration has something to do with the change in the specimens?

have you established that it could not have been something else, like bynesian decay?

link

In a safe (due to lack of space elsewhere) I have some in drawers and the same thing has happened to them.

Hydration is the only thing that I could think of that has changed. The fossils came from the bottom of valleys (in wet-weather creeks), and it is either wet or moist all the time there. In a safe (with desiccant, of course) there is no light (so no sun damage) and very little moisture. I have had many shells of (current) mollusks that have had Bynesian decay, and this doesn't appear to be anything like that. The best way I can think of explaining it is it's like doughnut glaze. When it's fresh, hydrated and warm, it is clear. As it dries out, it becomes creamy, then an opaque white.

I'm not saying that it can't be something else, I'm just saying that the decrease in water content is the only thing I can think of. I've been leaving new specimens in the field (though in a convenient place) until I can find out whether or not I'm damaging them permanently by taking them out of their... umm... habitat? lol