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Peat Burns

Someone brought in this nice steinkern of a large gastropod found last week in the Middle Devonian Columbus Limestone near Columbus, Ohio.  It is likely Pleuronotus decewi.  Because I don't yet have this taxon (nor any palaeozoic gastropod taxa of that size), I took the opportunity to mold and cast it.

 

Here is the fossil:

 

Resized_20190321_021245_5964.thumb.jpeg.7cb53a2023b922da54732b7f20dc4c2c.jpeg

 

Here is the fossil (lower) and two casts I made (above).  These have a base-color that was added to the casting medium, but no color matching paint treatment has yet been applied (these are hot off the "press").

Resized_20190320_234623_7031.thumb.jpeg.7b0c3c6dc8aa68fb7aa5e7cdec09ebd3.jpeg

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Wrangellian

Interesting...

This is a fossil that doesn't belong to you, I gather?

Is it possible to make a cast without bubbles if more care is taken, or is that an unavoidable feature of the process? I've never tried casting fossils, myself.

Also, it looks like you put the 'intake' hole on the surface of the snail. Would it not be better to put that on a non-fossil surface, if you know what I mean, such as at the the aperture where there is just matrix?

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Kane

*Adds a few Paleozoic gastro steinkerns to Tony's gift box* :D 

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caldigger

Tony, what is the "medium" you cast these out of?

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Plax

very interesting. Is this a steinkern?

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Ludwigia

@Peat Burns Yes, I'd also be interested to hear from you in more detail as to how you make your casts and what material you use.

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Tidgy's Dad

Agree with all of the above. 

Very interesting and more detail is required of the process. :)

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Peat Burns
8 hours ago, Wrangellian said:

This is a fossil that doesn't belong to you, I gather?

Yes, that is correct.  The collector kindly allowed me to borrow it to make a cast.

 

8 hours ago, Wrangellian said:

Is it possible to make a cast without bubbles if more care is taken, or is that an unavoidable feature of the process?

Bad technique on my part.  It is definitely possible to reduce their numbers far better than I did on this one.  It's a balance of making sure the casting medium is stirred thoroughly and not stirring so vigorously that you generate bubbles.  Then slow, careful pouring is also helpful.  Eliminating all tiny bubbles is probably next to impossible. Those can be filled after the cast is made.

 

8 hours ago, Wrangellian said:

Also, it looks like you put the 'intake' hole on the surface of the snail. Would it not be better to put that on a non-fossil surface, if you know what I mean, such as at the the aperture where there is just matrix?

Yes, especially on a cast of an "important" fossil.  On these fossils with simple morphology that are "quick and dirty", I don't make a pour hole.  I just pour the mold medium over the entire fossil and after the mold dries, a make a slit with an xacto knife and pop the fossil out through that slit.  To cast, I open the slit, pour in the medium, and the slit seals right up, usually only leaving a very tissue-paper-thin flange that can be picked off.  This method eliminates the need for making two separate mold halves.

 

8 hours ago, Kane said:

*Adds a few Paleozoic gastro steinkerns to Tony's gift box* :D 

:yay-smiley-1::notworthy:

I'll see if I can bring anything you guys might be interested in as a thank you.

 

7 hours ago, caldigger said:

Tony, what is the "medium" you cast these out of?

 

5 hours ago, Tidgy's Dad said:

Agree with all of the above. 

Very interesting and more detail is required of the process. :)

It is a two-part epoxy-type casting medium.  I get it from Alumilite Corp.  The molds are made with high strength silicone rubber.

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Peat Burns

@Wrangellian, @caldigger, @Tidgy's Dad

 

Here are a couple other examples.  I don't claim to be an expert on casting and am 100% self-taught on this endeavor, so take the info for what it is worth!:)  Some of these were "quickies" for teaching specimens on which I didn't spend a lot of time color matching, etc.  (I do exercise much more care and caution when making casts of important fossils and try to reduce as much as possible any bubbles, obscuring of fossil surfaces, etc., etc.)

 

Note on the Mesohippus jaw (which is right out of the mold and not painted) that even the gloss finish on the enamel is recorded by the mold and casting medium...

 

5c93c8b5b6c6c_BivalveFossilandCast.jpg.d2eb424bd42fa27f2baf7b982d0ecced.jpg

PlatycerasDumosusRarispinaFossilandCast.jpg.a9131234c4ad2ee39a5fdf4bd9c0c717.jpg

20170627_210959-1.jpg.7bfbcd62f705668b4bd7064f0b3971ec.jpg

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Peat Burns

@Wrangellian, @Tidgy's Dad

 

Here is a picture of the snail mold showing the slit I made.

20190321_133106.jpg.dbed4a9962eab0e26161dafacb81c973.jpg

 

Here you can see how well the slit "seals up".

20190321_133136.jpg.dce85318b64eaecefddb82a60cc5daec.jpg

 

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Peat Burns
7 hours ago, Plax said:

very interesting. Is this a steinkern?

Hi Plax.  Yes, this is a steinkern.  I can't find any sources that show this taxon as anything but, so I think it is typically found only as Steinkerne.  I think the morphological features of the steinkern (especially the body whorl), the relative size, stratigraphic position, etc., allow reasonably reliable identification of this taxon despite having no external shell features.

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