A little experiment in go slow.

[Malcolmt]

I have been meaning to do this little experiment for some time. Normally an essentially complete trilobite from Penn Dixie in upstate New York will take me about 30 to 40 minutes to prep. Prepping one of these is relatively easy and generally gives decent results. The dark black trilo against the grey matrix always comes out nice.These trilos (eldredgeops) are about as common as I can collect and I probably have hundreds in buckets that might get prepped someday.

So for the experiment I took a trilobite that was essentially complete and substantially covered with matrix. This was an extremely inflated specimen that just had a couple of defects in a few pleura. The experiment was to prep the trilo from starting to end using only the best techniques that I would generally reserve for a much better specimen than this one.

The normal 30 - 40 minute prep would look something like this all done under a scope at about 7x magnification using a Comco MB1000 air abrasion unit

Air scribe using an ARO till trilo is pretty much exposed

Any remaining air scribing with a Pferd using fine stylus

Initial air abrasion using a .040 nozzle and 80 micron dolomite

Bulk air abrasion using .030 nozzle and 80 micron dolomite

Final air abrasion and clean up using .018 nozzle and 40 micron dolomite

The Experimental Prep

All prep done under a scope at up to 40x magnification

For this one air scribing was limited to using the Pferd with a fine stylus

All air abrasion was done with .015 and .010 nozzles using sub 40 micron dolomite

Max PSI used was 18 PSI and went as low as 3 PSI in the eye area under 40x magnification

The difference

It too 6 hours from start to finish and I think it looks fairly decent. Actually still needs a bit of cleaning with a fine toothbrush to get out a few bits of fine dolomite powder in the crevices... Note there is no restoration or repairs of any kind on this trilo. Has a nice pyritized burrow off to one side going under the trilo.

Not the best photography here just with my cell phone...

2nd and 3rd pleura damaged on this side as well

Edited January 29, 2016 by Malcolmt

[Malcolmt]

NIce little burrow going under the trilobite

Edited January 29, 2016 by Malcolmt

[Malcolmt]

2nd pleura is damaged

Edited January 29, 2016 by Malcolmt

[Auspex]

That's a real gem, Malcolm. When magnified, I'm guessing that the resulting appearance owes something to retained fine details?

[Malcolmt]

Under high magnification (40x) with a very small nozzle size .010 and sub 40 micron dolomite you are literally abrading between the tubercles without any overspray touching then . When dropped down to a very low PSI with the minimum powder flow on the Comco you are literally abrading grain by grain. It just takes a heck of a lot longer to do . One of these days I will rig up a camera stand for my Nikon SLR so that I can take some pictures with a high f stop and good depth of field.

Edited January 29, 2016 by Malcolmt

[Fossil Claw]

You sir are an artist.

I hope to be half as good as you some day.

[Fossildude19]

Excellent result, Malcolm!

Thanks for the walk through.

Regards,

[Ludwigia]

The proof is in the pudding

[jpc]

So, will you be doing them all at slow speed now? Is the difference noticeable?

Edited January 29, 2016 by jpc

[Lmshoemaker]

Wow, the extra time and precision makes a noticeable difference. Fantastic job.

[Ptychodus04]

Can you post a photo of a quick prep specimen for comparison with your slow prep technique?

[Malcolmt]

JPC, I believe there is a difference, is it worth probably an extra 5 hours effort probably not. These trilos are relatively common and unless it was a pristine museum quality specimen nicely laid out I would not think it worth the time.

Economically, lets say that prepping is worth $25 to $30 per hour if you add the time and gas of collecting the fossil then the lower quality prep would likely give a return for effort value to the bug of about $40 - $50 which is in line with what I would feel one of these is worth. Now if we took the much higher quality prep then you would need to get $190 - $200 to get the same type of return for effort. Way over priced unless this was an absolutely pristine museum quality piece on the larger size for one of these eldredgeops.

So will this become the norm for me on common fossils. No

On unique pieces.... most definitely

I am going to go down into the basement this morning and prep what I think is a similar specimen using the lower quality prep scheme. I will post some pictures in this thread to let you see.

[Malcolmt]

Just went down to the prep lab here is the bug that I am going to prep using the lower quality techniques (this is still not horrible technique just not as high precision). I suspect it is a similar size and in similar shape to the other one (30mm * 16mm). This one appears to be 17.5mm wide and is likely over 30mm long.

[Malcolmt]

All prepping of this bug is being done at 7x magnification. I never prep with using a scope. Using a scope makes a world of difference.

Here is the bug after 2 minutes of air scribing but no abrasions. At this point I am not sure that it is a complete bug we will know in the next few minutes as I am about to do some air abrasion with a .040 nozzle and 80 micron dolomite.

Edited January 29, 2016 by Malcolmt

[Malcolmt]

Ok so here it is after 3 minutes of abrasion with a .040 nozzle at 62 PSI (so 5 minutes total time) . Obviously this specimen is not prone after all but is partially enrolled. Will need to decide how to sculpt the matrix a bit so that it presents a bit better . Could still turn out to be half decent. Normally I might have put this one aside at this point because there is just nothing that special about it from what I can see so far.

Time for a cup of tea first though.......

Edited January 29, 2016 by Malcolmt

[Malcolmt]

Ok so a few cuts with a diamond saw about 5 more minutes with an ARO air scribe and about 3 more minutes of .040 nozzle abrasion at 62 PSI gets us to the 13 minute mark. It appears that the bug is complete (you cant see the back that I have partially exposed). There is a nice pyritized burrow going under this one as well . Working towards a finished specimen that is floating off the matrix exposing maybe 75% of the bug. Could turn out to be a decent bug.

Edited January 29, 2016 by Malcolmt

[Malcolmt]

OK status update on the lower quality prep at 10 additional minutes of air scribe work and .040 nozzle abrasion still at 62 PSI (We are now at 23 minutes and counting) Unfortunately at this point the front middle of the cephalons exoskeleton separated from the trilo. You can see in the previous picture where the front of the cephalon on this specimen had the crack faults going through it. Sometimes on trilos that look like the are not going to stay together during the prep I will wick in very thin cysnoacrylate into all the cracks before starting the prep. Did not do this for this one as I thought it looked pretty solid and I generally only use consolidation techniques when I have to. My preference is always for no repairs or restoration unless it is absolutely necessary. Had to open up the blast box and sieve the abrasive powder then find the missing two pieces. After about 40 minutes of looking I did find both pieces (normally I would not even have bothered the bug would just have gone into the B grade fossil drawer ) Currently waiting for the cyanoacrylate to cure a bit before I resume prep. What is interesting is that there is quite a nice pyritized burrow on the underside of the fossil matrix which I will try to retain

Having lunch then will go finish it off with a combo of .030 nozzle and perhaps the .018 to clear out some of the furrows.

Edited January 29, 2016 by Malcolmt

[Auspex]

The signal I am getting is that you are settling in for a long winter...

I love it when you showcase your skills!

[Malcolmt]

Ok I put in 16 minutes of abrasion with a .030 nozzle at 40 PSI using 80 micron dolomite since the glue repair dried bringing us to a total time invested of 39 minutes. Other than perhaps a tiny bit of cleanup if I get in the mood this one is probably as done as it is going to get. Its redeeming feature is really the nice pyritized burrows that are associated with the fossil.

Overall from the from it looks like this

Edited January 29, 2016 by Malcolmt

[Malcolmt]

Overall from the back it looks like this, note that there is a second inverted enrolled trilo on the back that I took the time to uncover. Also a cool looking burrow.

Edited January 29, 2016 by Malcolmt

[Malcolmt]

Closer up from the front

Note the repair at the middle front of the cephalon.

Also note that with the larger .030 nozzle size that I could not get all the matrix material out of the small crevasses

Here is a close up of the eye (just using my cell phone)

Edited January 29, 2016 by Malcolmt

[Malcolmt]

Closer up from the back

To me there is a world of difference between this a lower quality prep and the higher precision prep in the first trilobite. The features just are not as crisp and the end product is a little duller and just doesn't pop out as much as the other one. End result is still a decent trilo particularly with the burrows and the associated horn coral and the inverted smaller eldredgeops on the back side. If I had done a low pressure prep under 10 PSI using only .018, .015 and .010 high precision nozzles then I likely would not have had the exoskeleton come off the cephalon necessitating the repair. Regardless I would never have put 5 plus hours into prepping this specimen as it from the start was obviously not going to be a museum quality piece.

Anyway hope you found this little post somewhat informative gives you some sense what goes into a prep on something that was never going to be museum quality.

Edited January 29, 2016 by Malcolmt

[Ludwigia]

Thanks for doing this experiment for our informational benefit. I agree with you on all accounts and make my prep decisions on a similar basis. There's no question to me that when the psi is high that the surface of the fossils comes out more dull than when they are lower and that sometimes fine details or loose-sitting parts can be blown away. Depends on the relative hardness of the fossils themselves to a great extent, and that's a matter of experience. You generally have a good idea beforehand which way to go, but sometimes you're in for a surprise when you go for high pressure and part of the fossil suddenly falls apart irreparably. That's ok when the quality wasn't so good to start with, but if I'm working on something where I think it could even be interesting for scientific study or which could turn out to be "museum quality", then low pressure, fine scribing and magnification are prescribed.

By the way, do you know what might have created those burrows?

Edited January 30, 2016 by Ludwigia

[Malcolmt]

I wish I knew what created the burrows. You find pockets in which almost every trilobite fossil at Penn has at lest some pyritized burrow segments in it. I have always thought it was a worm of some type but that is sheer speculation on my part. The burrows all seem to be similar in diameter. I have googled the subject and really could not find anything very specific.

[Ludwigia]

Did you try asking Jerry? Maybe he has an idea.