Help needed: Fossil crab claw prep. Matrix not coming off

[Jon C]

My son found a fossilized crab claw in western Washington State and I'm having a lot of difficulty prepping it.  I have a Dremel with a carbide fossil prep tip (very basic tools), but when I get close to the claw shell, the matrix is not coming off cleanly and I'm worried that I'll destroy it.  I've previously prepped some ammonites with the same tool and the matrix just popped off at the shell.  The matrix seems to be very hard sandstone and seems to get more dense closer to the claw.

 

Does anyone have suggestions as to how I can prep this?  Is there like an acid or something I can do to weaken the bond between the matrix and claw?  Is there another technique to separate 

 

I attached some pics where I started to prep, but the only part where the claw is sticking out is the very tip (small tan area in the Tip pic).  The dark line in the pics is super glue where I had to glue the two pieces back together when I split the claw as a cross section.  I could see by the cross section that the claw shells is very thin.

[Jaybot]

@RJB Might be able to help.. I've only attempted to prep some WA crab material, and quickly gave up since I didn't have the skills at that time.

[RJB]

Hello Jon C.   There is a way to handle a 'sticky' project.  Sticky is what we call it when the rock doesn't pop that way we would like.   You use the side of the tip/stylus and literally wear off the rock.  You do damage the specimen but trying to use the point of the tip will be much worse.  If you have time try looking up "Prepping a Family of Crab.  This is Baby Crab - Part 1 of 3" on You Tube, my channel name is RB Fossils.  That video might give you a good idea what to do.  I wish you the best of luck

 

RB

[Kane]

Great advice on stickiness, as many of us have been there and what looked like a 2 hour job turns into 20 in a hurry! RB's method for grinding down is perhaps the best chance. Alternatively, I've found patient and careful scribe "kissing" can also help, but that is a kind of removal grain by grain, and it requires very good hand control (if going that route, it is best to rest your scribing hand on something). In any case, the old SLAM acronym applies as you prep. It is important to take frequent breaks. SLAM = stop, look, assess, and manage. 

 

Good luck! Doing crab concs is perhaps one of the most advanced forms of prep. I know professional prep folks who have been at it for several decades that won't go near them, so those folks like RB are truly a cut above.

[Jon C]

Thanks for all the advice.  Hopefully I won't destroy it or do too much damage.   I'll post a pic if it's semi-successful or an RIP if it doesn't make it.  It's just a single claw, so not the end of the world.  If anything, I'll get some practice and knowledge out of it.  

 

The other bit of knowledge I gleaned from this trip was what is NOT a fossil bearing concretion (we're newbies).   My son and I managed to misidentify a bunch of non-concretions which contained nothing and were way too hard (probably ancient volcanic ash).