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holdinghistory

Cleaning up dolomite? Mosasaur project

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holdinghistory

I started working on a Mosasaur snout end, and so far it is coming well. I have been running into one issue though with starting to use a sandblaster, and that is that I can't figure out how to clean the extra dolomite off the piece when I am done. I have tried blowing it off with an air compressor, which gets most of it, and using water, which has caused some problems. The water seems to get into cracks and destabilize the matrix, leading to breakage. Any ideas?

 

On this one it dissolved some elmer's glue that was used in a repair, and on some trilobites it broke the matrix.

 

Thanks!

Nathan

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Progress so far.

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snolly50

I would simply remove the granular matrix with a carbide needle and pin vise. The matrix will "scrape" away. There is no use to abrade it. I assume this is a Moroccan piece and that matrix is very amenable to removal with non-powered tools. The "blaster" approach is, I believe, a less than optimal technique for this piece. Good luck, have fun.  

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holdinghistory

It actually seems to be working very well to get the tiny pieces out of the pores, just leaving a dust behind. I removed a lot of the bulk matrix with an air scribe.

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snolly50
12 minutes ago, holdinghistory said:

It actually seems to be working very well to get the tiny pieces out of the pores, just leaving a dust behind. I removed a lot of the bulk matrix with an air scribe.

Excellent. I believe the simple hand-powered prep I attempted to describe would be just be quicker and more effective. However, the best technique is the one that works best for any individual. Have fun, nice snoot, by the way.

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RJB

Im with snolly on this one.  I dont belive this piece was a good candidate for the sandblaster.  But good luck.

 

RB

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holdinghistory

You guys definitely know a lot more about it than I do. What would you use for a final cleanup then, a brush?

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holdinghistory

Another question I would have then is when is the use of an abrasive unit the best means of prepping? I am a bit newer to this, so lots to learn still ;-) 

 

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snolly50
16 minutes ago, holdinghistory said:

Another question I would have then is when is the use of an abrasive unit the best means of prepping? I am a bit newer to this, so lots to learn still ;-) 

 

I think you are off to a great start. The Mosasaur piece you are working on is going to be a wonderful specimen when you are done. To my eye it is impressive already.

 

To me using the abrasive technique here is overly complicated. The sandy matrix is harder than the dolomite. So instead of eroding the sand it is mechanically "ungluing" it with impact force. It would seem that direct mechanical force ("scraping" with a pick or carbide needle) would be a more direct path to the same end.

 

I am not a big air abrasive guy (check out the prep topic for lots of insights); but I think a general guide for use would be - removal of a thin coating of material from a fossils surface. The "blasting" agent employed would ideally be harder than the material to be removed, but softer than the fossil.  

 

Here is the link to the Mosasaur prep I recently posted - same type of matrix. The approach is just my method. others may have a superior technique.

Good luck, most of all have fun.

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holdinghistory

Gotcha, that makes sense. So that is why an abrasive unit is good for trilobites, since the bug shell is so hard, with softer shale material typically for a matrix. 

 

Nice job on the jaw, I was the underbidder on that one ;-). 

 

Per your guy's advice I am proceeding with the manual prep. When I got started again, I was able to solve the mystery. I started out with a carbide scribe pen (not pneumatic, used to engraving glass and such) and an air scribe gently on the thick areas. The dirt was just not coming off well, so I switched to my abrasive unit which seemed to work really well where the scribe didn't. After washing off the powder it still looked white, but it wasn't only the dolomite, it was the elmer's glue they used to repair it. After getting it wet, the dirt came right off with the needle since the glue consolidating it and holding it to the matrix was dissolved. The white also was also mostly removed. I thought I was damaging the bone with the scribe which is why I tried the abrasive. I wasn't actually damaging bone, I was just removing glue with the dirt. There was pretty much watered down glue over the whole piece that was holding dirt on. Once I dissolved it all the dirt came off easily. 

 

So moving forward I completely took the piece apart where they did repairs so that I could redo it without the matrix in between. Unfortunately one of the teeth coming in was broken and held in place by the matrix, but I found a second one that was not originally visible on the other side. We will see how it goes now.

 

Nathan

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jpc

Unlike our friend snolly, I am a big fan of air abrasives.  The best way to remove dolomite powder is to empty out the air abrasive machine and use the empty tank to blow away the dolomite.  For some reason (focused jet?) this works much better than just compressed air from the end of the air line. 

 

On the other hand, I know nothing about prepping Moroccan materials.  Nice piece.    

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LordTrilobite

I always prep my Moroccan mosasaur material by hand using dental picks and stabilizing them with cyanoacrylate where needed. I don't think I'd use air abrasion on these types of fossils as the bone is generally quite soft.

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holdinghistory

Thank you! I have it all finished up now. I took apart the repairs and prepped the rest of it by hand with a carbide pen. It is all back together now.

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snolly50

It looks fantastic. The texture of the bone is striking. The presence of the replacement teeth makes it all the better. Great prep job.  

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jpc

beautiful

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Xiphactinus

nice piece! Super preparation.

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holdinghistory

Thank you! I was really happy to find the replacement teeth hidden in the matrix. 

 

On 10/13/2017 at 4:55 AM, LordTrilobite said:

I always prep my Moroccan mosasaur material by hand using dental picks and stabilizing them with cyanoacrylate where needed. I don't think I'd use air abrasion on these types of fossils as the bone is generally quite soft.

 

Is there a particular type of cyanoacrylate you use?

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LordTrilobite

That's very striking indeed. Great job on the prep.

 

1 minute ago, holdinghistory said:

Is there a particular type of cyanoacrylate you use?

The thinner the better, so that it flows into all the cracks nicely. Otherwise I don't think it matters much which brand you get. In my experience the effect is the same.

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Aurelius

I'd not really considered abrasion on this material before, but it looks like you had good results. Could be very useful for final cleaning of a piece, just to remove those tiny grains that are hard to remove individually.

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holdinghistory

I actually finished by hand, the air abrasion was earlier. It did get the little grains out, but I am inclined to agree with some other members that it was not an optimal technique for this type of material.

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JohnBrewer

Wow, that’s a superb end result, well done!

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