Very Small Trilobites

[Kalo]

Hello, what would be the best way to clean these small trilobites?

The needle comes too big and I do not have air blaster yet...

Thank you in advance!

[DeepTimeIsotopes]

Rotating dremel tool perhaps?

[Ptychodus04]

On something that small, I would use acid. Very dilute and for short periods of time. Soak, scrub, rinse, repeat. The matrix looks like calcite on limestone. Is this correct? If yes, 5% acetic acid (vinegar) should do the trick.

[Kalo]

Thank you both!

I will try with acetic acid and upload pictures later.

[funfordds]

I would avoid using a dremel. it will likely strip the shell off the trilobite before you even know it. dental picks along with acetic acid should do the trick.

[Kalo]

And here I have a little problem:

when I keep the stone in a acetic acid,

the whole side become fade, specially the fossil lose colour.

Can I restore the first colour, somehow? or how I can avoid this...?

Edited November 9, 2014 by Kalo

[Ptychodus04]

What was the strength of the acetic acid you used? I've never had 5% (vinegar strength) bleach a fossil. Stronger acids always discolor the material. You can use oil to darken the fossil in order to try to bring it back to the original color.

[Kalo]

I used apple vinegar 5%

on the picture below (attached by Auspex)

you can see the difference between the one diped in vinegar (right) and another piece from the same rock (left)...

Edited November 10, 2014 by Kalo

[Auspex]

[tmaier]

It is unlikely to be "bleached". It is more likely that the dark was organic stuff on the surface, and the vinegar removed a very thin layer of limestone from the surface with the organic schmutz attached. It undercut it. You can see if that is true by scratching the dark one and see if the scratch is light colored.

Oh, I always use "white vinegar". It has fewer other things in it, other things like strange organics that may yellow later on.

Edited November 10, 2014 by tmaier

[Kalo]

Thank you all!

[Ptychodus04]

It is unlikely to be "bleached". It is more likely that the dark was organic stuff on the surface, and the vinegar removed a very thin layer of limestone from the surface with the organic schmutz attached. It undercut it. You can see if that is true by scratching the dark one and see if the scratch is light colored.

Oh, I always use "white vinegar". It has fewer other things in it, other things like strange organics that may yellow later on.

I concur.

[tmaier]

Another tip about delicate work with acid is to not get over aggressive with soaking the specimen for a long time. For small delicate items, brush some on with a small artist's paint brush and then brush it off within seconds or minutes. Dab with a que-tip swab to absorb it off quickly. Watch carefully.

When finished, you can neutralize the residual acid by using some baking soda mixed in water. This becomes an acid stopping agent. Mix about 1 teaspoon of baking soda in a half cup of water. Allow excess soda to settle, and brush the fluid onto the fossil, then rinse with water, then repeat. Sniff it to make sure you no longer smell the acidic oder. If you just etch and then don't neutralize and flush, you run the risk of having delicate jobs continue on while you sleep, only to find that the acid has done some damage over the night.

And to prevent the acid from seeping in too deep for porous rock, you can presoak the specimen in water to keep the acid on the working surface.

[Ptychodus04]

Another tip about delicate work with acid is to not get over aggressive with soaking the specimen for a long time.

Great minds think alike. From my earlier post "On something that small, I would use acid. Very dilute and for short periods of time."

I have ruined fossils by soaking them too long. My worst offense was a Ptychodus whipplei tooth that was an inch long and a beautiful, shiny black color. After I got done it was a dull gray... So sad.

[Kalo]

...soaking the specimen for a long time.

There are things man learn by experience,

I learned another lesson.

p.s. I am in the Fossil world from a really short time,

still on a,b,c ...

Edited November 13, 2014 by Kalo

[tmaier]

I have a long background in laboratory procedures, so one of the first things you learn is to play around with your materials and methods first to get an idea how they behave, before working on the real item.

Just for an experiment, I took a echinoid in limestone and let it soak overnight in vinegar. I found the strangest marks on the test the next day. The bubbles that formed on the bottom would roll up the side and dig channels in the fossil. The bubbles were probably grinding abrasive particles into the surface as they ran up the sides from below. It created artifacts in the test that looked like part of the fossil.

[izak_]

I would (If it is limestone/ calcite) put it in a little bit of vinegar. Leave in there until the calcite/limestone is gone. Soak it in water for good 24 h or so and see how it looks! Try this technique on something else first and see if you are happy with it.

[tmaier]

I would (If it is limestone/ calcite) put it in a little bit of vinegar. Leave in there until the calcite/limestone is gone. Soak it in water for good 24 h or so and see how it looks! Try this technique on something else first and see if you are happy with it.

The whole fossil is calcite/limestone. I think he wants to have some fossil left, and not just a clear liquid for his collection.

[FossilDAWG]

Personally I would try the acid on a specimen I would not care about if it is damaged first, to see how it works. If the fossils are not silicified they may be as susceptible to the acid as the matrix is, or at least lose a lot of surface detail. Bone (which is largely calcium phosphate) may be more resistant than calcium carbonate, which often replaces trilobite shell (the original chitin is long gone).

For such specimens I usually use a very small, sharp instrument; usually I find syringe needles work well. Your needle is much too blunt. Syringe needles have a very fine sharp point, but they also are blade-like to the sides of the actual point. I use these surfaces to apply pressure to the rock close to the specimen, so as to cause small pieces to flake off of the specimen. Often this means applying pressure towards the specimen, so you have to be very careful that the needle doesn't jump forward and damage the fossil when the matrix flakes off. Applying the pressure in a direction that is a tangent to the specimen, rather than directly towards it, can help avoid damage. Of course this is done under a binocular microscope and requires practice and a steady hand.

In Richard Fortey's book "Trilobite" he describes how he used phonograph needles to clean his trilobites when he was a grad student. The concept is the same. His fellow grad students used to joke that he was actually carving trilobites and not just cleaning them.

Don