Plant fossil prep help

[dolevfab]

I have plant fossils that I want to prepare. The plant remains occur in a thin ferruginous fine-grained ferro-alumosilicate layer. The fossils are covered with calcium sulfate crystals. Those obscure the fossil. It would be a great help if someone could explain how to remove them! I could not find a way to dissolve them, so painstaking manual removal with a pin is the only option i found...

In the picture you can see the row of leaves (bennetittales) with the white crystals on top. 

[Harry Pristis]

 

Low-velocity glass beads from an air-abrasive machine will remove the crystals.

 

 

[dolevfab]

1 minute ago, Harry Pristis said:

 

Low-velocity glass beads from an air-abrasive machine will remove the crystals.

 

 

Since I can't buy an air abrasive machine I guess I will just leave it outside when the summer sandstorms hit.. 

[Ptychodus04]

On 12/26/2017 at 10:10 AM, dolevfab said:

I have plant fossils that I want to prepare. The plant remains occur in a thin ferruginous fine-grained ferro-alumosilicate layer. The fossils are covered with calcium sulfate crystals. Those obscure the fossil. It would be a great help if someone could explain how to remove them! I could not find a way to dissolve them, so painstaking manual removal with a pin is the only option i found...

In the picture you can see the row of leaves (bennetittales) with the white crystals on top. 

 

 

Since the matrix is not calcium based, most acids should have an effect on the calcium sulfate without dissolving the matrix. Do you have several specimens that you can experiment with? I'm going to assume you have experience working with acids and know to do so with proper safety gear in a well ventilated area, always adding acid to the water when diluting, etc.

 

I would start with 5% hydrochloric and soak a sample to see what effect it has on the CaSO4 as well as the matrix and fossil. If the hydrochloric has a deleterious effect on fossil or matrix, try 5% acetic acid (vinegar).

Edited December 28, 2017 by Ptychodus04
Homer Simpson moment

[Ramo]

Ptychodus,  I'm sure you meant to say  "Always add acid to water".  (Not water to acid) when diluting.

 

[Ptychodus04]

8 hours ago, Ramo said:

Ptychodus,  I'm sure you meant to say  "Always add acid to water".  (Not water to acid) when diluting.

 

 

Yes, thank you for catching that. Dyslexia strikes again.

Adding water to acid can be very dangerous because it can set off a rapid exothermic reaction, causing the acid to explode out of the container.

[RJB]

Would be interesting to see a before and after picture?

 

RB

[paleoflor]

Sulphates are very stable in acidic environments (you would have to go against the dissociation of sulphuric acid to dissolve the calcium sulphate in acidic environments - unlikely). Instead, you could try to react your calcium sulphate with an alkaline fluid, such as a sodium hydroxide solution. This will transform your calcium sulphate into sodium sulphate (soluble) and precipitate calcium hydroxide and/or calcium carbonate (the latter by combining with carbon dioxide from the water/air). You will probably need to do this at elevated temperature, in order to get the kinetics up. The newly formed hydroxide/carbonate solids can (after rinsing to remove the soluble sodium sulphate to prevent re-precipitation of sulphates) be removed using acids. However, it is difficult to predict how the matrix minerals will respond to such a fluid treatment. Best to do a trial experiment first. Moreover, please do note that working with chemicals can be dangerous; proper precautions, including use of the necessary personal protective equipment, are needed before attempting something like an alkaline fluid treatment.