Fossil preparation / enhancement with the help of heat

[FranzBernhard]

I would like to ask if anyone has experience with fossil preparation with the help of heat. My question is triggered by that topic:

Authenticating quartz (?) Keichousaurus? - Is It Real? How to Recognize Fossil Fabrications - The Fossil Forum

My hypothesis is, that this specimen was baked (as a whole or only superficially, with a blow torch, for example, possibly several times) to promote flaking off of the matrix.

Could this be correct?

 

Another question: Some time ago, a baked crinoidal limestone was shown here on TFF (with color turned from a somewhat uniform gray to white-reddish), I can not find the topic again. Anybody else able to find it or able to point to a similar item?

 

Thank you!
Franz Bernhard

[Denis Arcand]

Hi @FranzBernhard,   I don't know if this is what you are looking for. I'm also interested in preparing fossils with heat, so let me know if you find anything 

 

 

[Roses]

@Denis Arcand That looks remarkably similar! Did some of the matrix flake off when you did that “bake”, to reveal more of the fossil structure? Or was it only a color change? I’m wondering why the prep quality is better on the couple white Keichousaurus specimens I’ve seen, relative to normal/un-treated ones, and if heating makes it easier to separate the matrix?

 

 

[Denis Arcand]

7 minutes ago, Roses said:

@Denis Arcand That looks remarkably similar! Did some of the matrix flake off when you did that “bake”, to reveal more of the fossil structure? Or was it only a color change? I’m wondering why the prep quality is better on the couple white Keichousaurus specimens I’ve seen, relative to normal/un-treated ones, and if heating makes it easier to separate the matrix?

 

 

In my case it's just a color change, bleaching the fossils and giving the matrix a much paler color, giving it a more sandy color

 

I believe @JohnJ is right when he says that micro-fracturing calcitic fossils causes them to reflect light differently.

 

I don't think that makes it easy to separate the matrix, at least not in my experiment. The brain more easily discerns the white fossils after the thermal process, which gives the impression that flakes are removed to show more fossils. It's just an illusion.

 

 

A fossil with a certain water content will emit steam which could flake matrix, but it could also cause your fossil to explode.

 

 

[FranzBernhard]

5 hours ago, Denis Arcand said:

 I don't know if this is what you are looking for.

Yes, perfect! That´s the topic I was looking for!
Thank you very much!

 

4 hours ago, Roses said:

makes it easier to separate the matrix?

It depends on matrix composition, temperature, temperature gradient, composition of the fossil etc.. For example, clay minerals of the matrix will give off water and may crumble easier then, but they could also melt, if too much heat is applied. Without personal experience, I would like to say, its a tricky business.

 

4 hours ago, Denis Arcand said:

but it could also cause your fossil to explode.

Yes, this could happen, its all trial and error at the beginning.

 

Franz Bernhard 

Edited December 17, 2022 by FranzBernhard

[Roses]

@FranzBernhard It looks like your theory of heat treatment is correct! But it sounds like a natural heating. I asked a paleobiologist who has published on these guys:

 

“Specimens of Keichousaurus are usually preserved in limestones. In general, the specimens with the blackish color are just exposed from the limestone outcrops, i.e., they was exposed either manually or naturally for a short period of time. In field, I often see those specimens on the surface of the limestones with whitish color, which means that those whitish specimens have been exposed by nature for a long time, being the result of prolonged exposure to the sun. Occasionally, in some limestones that are lightly marbleized also produce specimens with whitish color. According to its completeness, I think that your specimen probably came from the limestone experienced a light marbelization. Marble is formed by the recrystallization of limestones after the latter were baked by magma coming from the interior of the earth. Fossils in limestones should be fully destroyed during the crystallization. The limestone that your specimen is preserved is not fully recrystalized but jus slightly marbleized so that the fossils in the limestones are not destroyed but its original color changed during the light marbelization.”

[daves64]

20 hours ago, Denis Arcand said:

it could also cause your fossil to explode.

It's all fun & games until the fossil explodes, then it's @RJB prepping crabs with dynamite... Which is still fun & games! 

[cngodles]

Neighbors of mine, over several years, collected the fossiliferous limestone that drops from hillside erosion and created a large fire pit ring. They later abandoned it and I broke apart the slabs to get at the fossils.

 

The fire pit limestone was very brittle and easier to work than fresh limestone, probably a product of high heating and cooling several times over the years.