Penn Dixie Trilobite Preparation

[Reese the Rockhound]

I have several good Eldredgeops rana specimens from Penn Dixie Fossil Park, and they were fairly clean when I hacked them out.  Unfortunately, there is a lot of shale stubbornly stuck in the groves and crevasses of the trilobites.  I have access to a dental sandblaster, but I'm not sure if it's safe to use.  Any thoughts?

[Kane]

I use a Paasche with baking soda on PD bugs, and it works quite well. Practice on some less pristine pieces first, of course.

[Reese the Rockhound]

Is baking soda good for sandblasting because it is soft, or would fine-grained sand work just as well?

[caldigger]

I'd stick with the recommended mediums. Silica sands will likely blow a hole right through your fossil.

[Kane]

54 minutes ago, Reese the Rockhound said:

Is baking soda good for sandblasting because it is soft, or would fine-grained sand work just as well?

As Caldigger said, sand will destroy your fossil. 

 

Baking soda is softer than the trilobite shell, but can aggressively attack matrix, partially because the little crystals have sharp edges. For more stubborn matrix, you can add a bit of dolomite (9 to 1 ratio of baking soda to dolomite), but don’t jack the pressure beyond 40 PSI, and lower if possible. Slow and steady wins this race.

[Mark Kmiecik]

Is almond shell used in prepping fossils?

[Fossildude19]

6 hours ago, Mark Kmiecik said:

Is almond shell used in prepping fossils?

Haven't heard of almond shell media. 

Walnut shell media is used in normal sandblasting.

Not sure that the particles would be small enough to travel through an air eraser. 

[Kane]

6 hours ago, Mark Kmiecik said:

Is almond shell used in prepping fossils?

It would not work on PD matrix.

[Ptychodus04]

The trick with abrasives is to use one harder than the matrix but softer than the fossil. Iron powder is the exception to this rule as it removes matrix by percussion (spherical shaped particles) rather than cutting (irregularly shaped particles). 

 

Unfortunately, Iron powder costs around 10x that of dolomite or sodium bicarbonate.

[Mark Kmiecik]

5 hours ago, Fossildude19 said:

Haven't heard of almond shell media. 

Walnut shell media is used in normal sandblasting.

Not sure that the particles would be small enough to travel through an air eraser. 

I believe I was mistaken. I think it's walnut shell I remember used in sandblasting, but now that I think of it I don't see how it would be useful on any matrix tougher than chalk.

[Ptychodus04]

20 minutes ago, Mark Kmiecik said:

I believe I was mistaken. I think it's walnut shell I remember used in sandblasting, but now that I think of it I don't see how it would be useful on any matrix tougher than chalk.

It is walnut shell and you are correct, it would be relatively worthless for fossil preparation. Generally speaking, sodium bicarb is about the softest media used for fossil preparation.