Help with green river fish.

[Lmshoemaker]

Hello! When I bought my air abrasive a year ago the guy that I bought it from gave me a bunch of unprepped green river fish as he was retiring. One issue that seems to commonly come up is that no matter how low I set my psi or how slow I go on some fish the "skin" seems to pit and develop holes. Is there any way to avoid this? I've gone down to as low as 1-3psi with dolomite and this still happens. I've noticed that it tends to happen on disarticulated specimens mostly, and part of me feels this is more of a preservation issue than anything. The guy I got my abrasive from also included paint I'm assuming for this very reason, but I want to use it as sparingly as possible.

[Fossildude19]

I would think dolomite would be a bit too harsh for these. I would try using sodium bicarbonate at a slightly higher PSI. 

[FossilDAWG]

It's great that you were provided with some unprepped fish to practice on.  Generally you want to find an abrasive that is harder than the matrix and less hard than the fossil.  Dolomite is pretty hard/abrasive; sodium bicarbonate is more gentle and I believe it is (as Tim said) more commonly used for Green River fish.  @ptychodus and @RJB prep a lit of Green River fish and they perhaps could say more.  My understanding is that practice and technique are critical, and it's easy even for experienced preppers to occasionally burn through the bone on these fish.  I think the one you showed looks pretty nice!

 

Don

[RJB]

  One can use the handpiece held at an angle and use just part of the media stream to avoid those holes.  If doing so one might also not point the stream towards the outside of the fish but pointed inward to not aquire any media trails onto the rock.  Mind you, one may find it difficult when bones or areas are rather deep.  Good luck

 

RB

[Ptychodus04]

To add to what @RJB said, you want to scribe as close to the fish as possible before you move to abrasives. Often, you will burn through the fish when abraiding thicker material. Dolomite is definitely too hard for these fish. I switched over from soda to iron powder when I started prepping for one of the quarries. It is easier on the fish and can be used at really low pressures.

 

Sometimes, there's nothing you can do about the pitting. If you have fish that aren't well preserved, or if they came from the weathered edge of the quarry, they will be really soft and scale loss is eminent. Also, Diplomystus and Mioplossus have really thin scales that burn through easily. Priscacara, Phareodus, and Knightia all seem to have tougher scales.

 

EDIT: In looking back at your close up photo, it looks like you need to scribe off an additional 3 or 4 micro layers before you start abrasives. Are you using a microscope?

Edited September 13, 2021 by Ptychodus04

[RJB]

To add to what @Ptychodus04 said,  Kris is much better at explaining things than I am, thats for sure.  but here is a picture to show you that I take off as much rock as possible before I go on the air abrasive attack.  Good luck

 

RB

[Lmshoemaker]

Hey all, good recommendations. When I get back to working on it I will try some of them, notably using Sodium bicarb or maybe talc. I have a microscope but can't use it due to space limitations at the moment. That said it was also suggested that I scribe a little more. I have a microjack #4 which has had some issues since I got it. I might make a separate thread asking for help but might be able to get it here. The issue I have is when I get it up to the operating PSI of around 110-130, it sounds really rough (see attached video) stalls somewhat regularly, and when it doesn't stall the needle will ricochet off of the matrix aggressively. I have cleaned all the components I can, inspected for rust, checked the O-rings and haven't seen anything that should cause concern, but I am open to suggestions. Thanks all for your recommendations!

[jpc]

you can visually check the o-rings and not see any problems.  Go ahead and put a new o-ring in and see if this helps.  Also, you might need to mess with how tightly the head is screwed on.  This can affect the performance.     

[Ptychodus04]

I run my MJ 4 at 90 PSI and it seems to like it. No stalling issues. Definitely replace the o-rings and give the stylus and o-rings a light coating of 3 in 1 oil. Not so much as to make it wet or it will spray oil all over your fossils. If the performance issues persist, contact Paleo Tools and they will address it. They are really stand up folks.

 

On the scribe topic, you really want a bigger scribe for bulk matrix removal. The MJ will take you forever as it is a detail scribe. I take bulk matrix off with an ME9100 and/or an Aro depending on the thickness of the matrix.

 

A functional microscope is a must for detail prep work. It will allow you to scribe very close to the fossil without hitting it. With abrasives, it will allow you to remove microscopic bits of matrix without burning through the scales on the fish. This is almost impossible without a microscope.

[jpc]

4 hours ago, Ptychodus04 said:

I run my MJ 4 at 90 PSI and it seems to like it. No stalling issues. Definitely replace the o-rings and give the stylus and o-rings a light coating of 3 in 1 oil. Not so much as to make it wet or it will spray oil all over your fossils. If the performance issues persist, contact Paleo Tools and they will address it. They are really stand up folks.

 

On the scribe topic, you really want a bigger scribe for bulk matrix removal. The MJ will take you forever as it is a detail scribe. I take bulk matrix off with an ME9100 and/or an Aro depending on the thickness of the matrix.

 

A functional microscope is a must for detail prep work. It will allow you to scribe very close to the fossil without hitting it. With abrasives, it will allow you to remove microscopic bits of matrix without burning through the scales on the fish. This is almost impossible without a microscope.

all of these are great points.  I am also a big fan of the microscope for detail prep such as this fish.  I know one guy who does all of his dino bone prep under the scope as well.  Yay for microscopes.

 

[Ptychodus04]

15 hours ago, jpc said:

all of these are great points.  I am also a big fan of the microscope for detail prep such as this fish.  I know one guy who does all of his dino bone prep under the scope as well.  Yay for microscopes.

 

I don't put a tool to matrix without a minimum of 5x magnification.