Real or fake? rare fish from the US Eocene.

[mardopa]

27 minutes ago, Phevo said:

@mardopa

 

It looks like a replica to me, those are air bubbles, I'll go roughly through the process of making one:

 

You have an original (negative cast in this case), make a positive impression in silicone (soft material), then make a negative imprint (like the original) in Jesmonite or similar material(which is hard like stone).

 

Once you have the cast in Jesmonite you add colours and a varnish to finish it off

 

On a well made cast there are no air bubbles, that's why I wanted to see the back of your piece

And how do you explain the calcite microcrystals?

 

[FranzBernhard]

1 hour ago, mardopa said:

And how do you explain the calcite microcrystals?

Fill material? Like aggregate in concrete? But I don´t know how the matrix of the G-4 layer looks like.

Considering the air bubbles, which are clearly visible in side view, are such voids typical for the G-4 layer?
Franz Bernhard

[jpc]

3 hours ago, mardopa said:

 

This photo convinces me... this is NOT G-4 matrix.  G-4 matrix is much finer grained.  This is some sort of sandy/gritty compound used to make the cast.  

[aeon.rocks]

Cast 100%

[mardopa]

Hello
First, you have to take into account the magnification of the photo that can give a misleading perspective on the size of the grain.
On the other hand, I am not understood in that, but a compound like the one you say would form bubbles with air and above all, so much quantity. I know that plastics and resins do, but that other type of product seems strange to me.

[Fossildude19]

Concrete can have air bubbles.

Any substance which can be poured into a mold has the potential to have air bubbles.

[jpc]

1 hour ago, mardopa said:

Hello
First, you have to take into account the magnification of the photo that can give a misleading perspective on the size of the grain.
On the other hand, I am not understood in that, but a compound like the one you say would form bubbles with air and above all, so much quantity. I know that plastics and resins do, but that other type of product seems strange to me.

I do appreciate the magnification involved here, but in the G-4 layer it takes extreme magnification to see the grains.  I have never seen them in the fishes I have looked at.  This is a cast.  I am 99% certain, as sure as I can be without holding the fish in my hands.

 

 

[Phevo]

@mardopa The crystals could be from added material

 

The concrete I have used in my profession has 4-6 % of air in terms of volume which usually surprises alot of people. 

 

When concrete is used in less critical construction it consists of even more air, I'm not sure of the ratio in for example Jesmonite, but it would not surprise me if it is in the same range.

[mardopa]

Thank you all for your opinions and comments.

[LabRatKing]

On 10/11/2020 at 10:30 AM, Phevo said:

@mardopa

 

It looks like a replica to me, those are air bubbles, I'll go roughly through the process of making one:

 

You have an original (negative cast in this case), make a positive impression in silicone (soft material), then make a negative imprint (like the original) in Jesmonite or similar material(which is hard like stone).

 

Once you have the cast in Jesmonite you add colours and a varnish to finish it off

 

On a well made cast there are no air bubbles, that's why I wanted to see the back of your piece

Helps to have the vibrator table and the vacuum vessel for high quality casts!

[Phevo]

4 hours ago, LabRatKing said:

Helps to have the vibrator table and the vacuum vessel for high quality casts!

 

Yes, though it is best not advertised