Filling thin cracks in fossil bone

[Daze]

Does anyone know how to fill thin cracks in fossil bone? I'm not talking consolidating but esthetically retouching. I normally use Milliput epoxy (super fine white) for crackfilling and restoration, but I find it's too thick to easily fill thin cracks. Is there anything more thin/smooth and 'spreadable' to fill these thin cracks? 

[Ludwigia]

I don't know if Apoxie Sculpt is any better than Milliput, but that's what I always used for cracks. Just spread it and shove it down the crack with a very thin instrument until it gets filled up.

[trilobites_are_awesome]

I use milliput and have never had this problem!

I agree with Roger's assessment.

[CDiggs]

Both Paraloid B-72 and Butvar B-76 can be mixed with acetone to whatever consistency is required for gap/crack filling, is archival quality (unlike epoxy based fillers), can be tinted/colored with any dried pigment or even matrix, and most importantly is reversible -which is especially handy if any excess material gets on surfaces around said cracks to be filled. My lab doesn't let epoxies anywhere near real fossils anymore- only replicas.

[Daze]

Thanks, guess I'll just have to give it another try 

[hadrosauridae]

dont try to "shove" it into the cracks.  Take small balls of the epoxy and roll them out into long "snakes", then work those down into your cracks.  Use a wet finger to rub it in well, that will let you push it fully without it pulling back out as you work.  Scrape off the excess and finish with a wet paper towel and scrub the excess of the surface of the fossil, so that only the epoxy  remains in the crack.  Texture as needed.

[Ptychodus04]

46 minutes ago, hadrosauridae said:

dont try to "shove" it into the cracks.  Take small balls of the epoxy and roll them out into long "snakes", then work those down into your cracks.  Use a wet finger to rub it in well, that will let you push it fully without it pulling back out as you work.  Scrape off the excess and finish with a wet paper towel and scrub the excess of the surface of the fossil, so that only the epoxy  remains in the crack.  Texture as needed.

 

I use clay sculpting tools to work it into the cracks and remove any excess material before doing any texturing or smoothing. This keeps you from spreading it all over the surface of your specimen.

 

@CDiggs How do you deal with texturing Paraloid if using it as a filler? I imagine it's a pain. I use dry pigments to color my Apoxie Sculpt but your process is intriguing. We used Apoxie Sculpt regularly for restorations on specimens for public display when I was volunteering at my local museum.

[Jaybot]

8 hours ago, Ptychodus04 said:

 

@CDiggs How do you deal with texturing Paraloid if using it as a filler?

I'm wondering the same, sounds interesting.

[CDiggs]

20 hours ago, Ptychodus04 said:

@CDiggs How do you deal with texturing Paraloid if using it as a filler? I imagine it's a pain. I use dry pigments to color my Apoxie Sculpt but your process is intriguing. We used Apoxie Sculpt regularly for restorations on specimens for public display when I was volunteering at my local museum.

First, I should add disclaimers (probably should have from the start);

Using any of these materials and techniques does entail some degree of risk, acetone is not only highly flammable but also toxic, and anyone using it (or really any of these things) should be using proper PPE to prevent injury. Always take care and exercise caution, especially when handling unfamiliar chemicals.

https://www.nhsggc.org.uk/media/236208/msds-acetone.pdf

 

That out of the way, either Butvar or Paraloid can be textured or manipulated with a probe/pick/tool-of-choice during the setting process. As it solidifies it does retain some pliability for a time and the longer you let it set the less it tends to want to adhere to the tool. If I miss my window while its setting or decide I don't like my finished product, a short period of acetone fuming can soften the outer surface to re-texture or longer periods can be used to smooth the surface if the texture is too rough. Of course if you've used B-72 or B-76 as an adhesive to join any surfaces you need to be careful with acetone fuming, but so long as the specimen is well supported and the fuming isn't left too long the risk is low. Acetone fuming has become more common these days as a method for cold-smoothing PLA 3D prints so there are a number of how-to guides out there, but the basics include creating a sealed environment using glass, metal or HDPE acetone resistant plastic container, elevating the specimen in the container, place an open reservoir of acetone in there, then seal and monitor. For the love of god though, be sure to do this in an area with good ventilation away from open flames or sources of sparks. If you master fuming though it can also be used to increase the penetration of consolidants as well by slowing the evaporation of the solvent allowing greater migration into porous specimens or matrix.

 

A heat gun can also be used to soften or smooth either B-72 or B-76 as well, but of course comes with it's own hazards. As a bonus, both fuming and heat-guns can also be used to soften B-72 or B-76 when it's used as an adhesive allowing joins to be manipulated and re-set. Be careful when using heat guns with B-72 though, it can have a much lower glass-transition temperature depending on what solvents you use and the concentration it was mixed at. Like most restoration though, it's equal parts art and science. You may need to play around with set-times, preferred pigments and the like. I haven't been tinting or coloring any of our filler so far, our projects of late haven't been display specimens needing that level of aesthetic care and for potential research specimens I prefer that restoration be both minimal and immediately apparent, but I've been curious to look into marble dust as a pigment option that I've heard of for any display specimens we may need to tackle in the future.

 

Mind you, I can't claim to have pioneered any of this, I'm just relaying a little of what I managed to pick-up from this year's AMMP conference and some of their archived material.

[Ptychodus04]

Thanks for the info @CDiggs I'm going to play around with this. I use dry pigments designed for painters to make their own paint. It has worked well with Apoxie Sculpt and I would assume it will work well with Paraloid. I'm not excited about that mixing process with sticky Paraloid though.