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Hello everyone ! I have stored these crabs a couple of years ago, while storing them they cracked (I suppose it is due to the internal humidity, they were found on a sea coast). I have the paraloid to apply them, but there are these cracks that I have to fill somehow so the paraloid doesn't leak. What material do you suggest as filling? And please know what percentage of acetone and paraloid is in the mixture? Thank you all ! greetings ! ps: the material that covers the crabs is hard sand EDIT: The reality is that I don't have much of an idea of how to prepare them, I was thinking of applying a layer of paraloid on one side, also filling in the cracks on something (the one where the broken crab can be seen, the place where it was exposed) and working on it on the other side.

After a fair amount of research which paid off quite well for a beginner, I finally began to mesh some of the "bookworm" experience with the "on site blundering around in the desert until I got lucky" experience. The research said - large ammonites in this location. Okay. Many trips later, I suppose 6 inch diameter ammonites are considered Large. Found some, check. Another fossil collector's blog said the same thing so I went there. It just happened to be on the other side of the big ditch I was previously hunting in. Okay, the ditch was 20 plus miles wide with the Morrison Formation filling the ditch all the way to the other side. Turned out this opinion of what equates to a large ammonite was more in line with what I was thinking. 10, 12, 15, 20 inch diameter ammos sure fit the bill to me. When it takes two to carry one to their vehicle...yeah...you have a BIG ammonite. For me even the partials were amazing when just 3 or 4 chambers of an outer whorl were found. Doesn't take much to realize this 3 pound whorl section belonged to 350 to 500 mm diameter squid in a snail shell! Kinda like finding a Meg tooth or raptor claw...one definitely envisions the original owner's size. This is another chemical prep after gluing the loose parts securely. I used muriatic acid and a soft bristled toothbrush with a tub of water to rinse after each pass. This whorl section had been previously dug some years ago, IMO, and left behind. It has a few small lichen patches on the "back" side which I left as is. The largest lichen patch is 1 CM wide which equates to 1 mm a year's growth over 10 years of sunlight exposed rock. More or less. No other connecting parts were nearby when I collected it. I made one pass, rinsed, then a second pass with fresh acid followed by a rinse, repeat until the stopping point. As found. First pass. Second pass and rinse. Third pass and rinse. Final pass, rinse and stopping point. I was looking for some color contrast from before and after...or rather...coated with calcite and coating removed down to the "chocolate" with some areas still showing the calcite coating. Top view of the keel area. Backside with lichen patches showing. Drying after final rinse and inspection. Dry the next day. Freshly applied Paraloid coating. It cured out slightly less shiny except for the smoothest spots. Besides just liking these partial whorls of large ammonites, It's good practice for these guys awaiting preparation. The one on the right is a concretion of over 100#/45 + kg. The bucket on the left side has a 56 pound concretion with a 10-12 inch ammo in it. So the research boiled down to who considers what's big and what's REALLY BIG. I like them all but it was nice to find some that make me think I found something " DINOSAUR big" and not snail shell big.

Been using paraloid for a while now but I've found that it dries way too quickly making it difficult to achieve a smooth and consistent finish. I've heard I could use isopropyl alcohol instead of acetone which takes longer to evaporate which could be useful in allowing me to cover my entire specimens with an even layer. I was wondering if anyone else has tried this and if so I was wondering if there was anything I needed to know before trying this. I also wanted to ask about concentrations, at the moment I'm using a roughly 2% mixture to improve contrast and minimise that dusty look you get on many fossils on some brachiopods I found in Morocco. Is this the correct concentration? I hope someone can provide some insight here. Thanks.

Yes, I know it's non reversible and to clarify that I've used both Paraloid and white glue...the white glue water mixture was used ONCE to test it on a very flaky Green River Formation poorly preserved fish fossil. Otherwise I only use Paraloid. I was just tossing out to the OP a much less fume creating option. If I had a cat and a partial Oviraptor egg needing a protective sealant, I would leave the cat in the living space and take the fossil egg and Paraloid outside somewhere to coat it. Then let it evaporate and dry thoroughly before bringing it back indoors where the cat is. Win-win!

You can use Paraloid but cyanoacrylate is better in my opinion. If you want the Paraloid to penetrate the cracks well, the solution must be low viscosity - so little Paraloid resin and a lot of acetone (for example 5% Paraloid). When drying, the acetone evaporates and the Paraloid remains in the cracks. The cracks are therefore never completely filled with solid Paraloid resin - only 5%. Even if you repeat this several times, it won't get much better. If you use a higher concentration of Paraloid (say 30%), more resin is transported into the cracks and remains there after the acetone has evaporated - but only 30% of the volume of the cracks is filled with resin. On the other hand, the solution becomes highly viscous and therefore does not penetrate the cracks as well.. Cyanoacrylate has a low viscosity and shrinks only minimally during curing - it contains no solvent. The cracks are almost 100% filled with resin.

that doesnt exclude it from being used with Paraloid. Neither of those, in the quantities included affect Paraloid solution. And again, as long you arent trying to drink the stuff, its not going to be harmful.

I think you have gotten advice/choices as good as it gets. All the replies you need and just pick and choose. One thing I have and continue to experience is sometimes I miss the stopping point and apply just a little TOO much Paraloid and it ends up being a little TOO wet looking...too glossy. I could go back and hit it with straight acetone or scuff it dull....still pondering about doing that. Good luck!

Elmer's will turn yellow and brittle over the years. Is there an exhaust fan in your bathroom? Do the paraloid thing in the bathroom with the fan on and keep the cat out for an hour.

One option is Elmer's type white glue, mixed 50/50 with water and brushed onto the fossil. It does have its downsides as it doesn't age as well as Paraloid. But no toxic fumes. I have used both.

Paraloid b72 is soluble in ethyl acetate. While acetone (which also occurs naturally in small quantities in the body) is only poorly metabolized / broken down in the body, ethyl acetate is readily converted to acetic acid and alcohol in the body, which is further broken down in the body. Ethyl acetate is widely available in nature and is found in many fruits and is much better tolerated than acetone. In most nail polish removers, acetone has therefore been replaced by ethyl acetate (at least in Europe).

Isopropyl isn’t one of the better solvents for Paraloid B72. According to the data sheets, it will work but museum info I’ve read indicate it is only slightly soluble in isopropyl. I haven’t personally tried it. “Your results might vary”. I don’t use ethanol as a solvent, so everything I’m about to say is speculation and/or 2nd hand information… The slower evaporation time of ethanol vs acetone can increase penetration of the solution into the specimen. More time as a fluid gives it more time to travel into the specimen (if your specimen is porous at all). I’ve also read that ethanol results in a less glossy appearance. The sheen that you get is a result of a layer of Paraloid on the surface of the specimen. The greater absorption of the ethanol based solution reduces the amount of Paraloid that gets deposited on the surface. I use Paraloid almost exclusively during the prep process so, a longer drying time is not advantageous for me. It would only result in more debris getting caught in the wet solution.

Your math is correct. 5% Paraloid B72 and 95% acetone. The ratio does not need to be exact. I would not use cyanoacrylate for the crack repair unless you're ok with dealing with the matrix being glued to the specimen. Local application of paraloid won't adversely affect your glue joints.

thanks for answering ! Would it be a solution of 5% paraloid and 95% acetone? Would it be very liquid? apply super glue to the crack to fill and join, will the paraloid dissolve it and ruin the fossil, dissolving the glue that is in the crack and getting inside?

I would not recommend cyanoacrylate, unless you're ok dealing with matrix adhered to your specimens. It will soak into the matrix and bond it to the crab, makaing preparation very difficult. Mix up a thin solution (roughly 5%0) of paraloid and pour it into the cracks. Then take a thicker solution (consistency of warm honey) and pour it into the cracks. It's going to leak out but it will lock everything together. If your blocks need to be stabilized, you can go about it 2 ways, 1: direct application of thin paraloid to the back until it is hard enough to hold together. 2: make a 1/2 jacket with plaster and burlap to cradle the back of the specimen.

Paraloid itself can be used to fill in the cracks, just use more paraloid to acetone. The easiest way is probably to use super glue, it is quick and cheap.

+1! I paraloid all my grf fish… often while still prepping it to keep from losing pieces on parts I’ve already cleaned. Clean, paraloid, clean,repeat…

If you’re looking for an exact ratio, make your solution by weight. Paraloid pellets don’t compact well, so you’re going to get a lot of air in a volumetric measurement. That being said, the ratio doesn’t need to be exact. If you need a longer dry time, use ethanol as your solvent. I tend to go with a 2% solution (dissolved in acetone) in most scenarios. I keep a bulk jar mixed up at around 25% and dilute as needed. If you need to even out brush strokes, let your Paraloid fully dry and then brush on a little acetone. This will dissolve the plastic on the surface and can even everything out. If I’m applying with a brush, I start with the perimeter and work my way in, overlapping the strokes. If everything goes south on you, you can always remove the Paraloid with acetone.

I bought ammolite on a internet auction. Former owner attached the documents about the fossile, that says it's bought in 1995. But the fossil coating is too old, and peeled off in some places. So I tried to peel all coating off and make new coating. I thought coating would be made from paraloid b72, but it cannot be dissolved by toluene and it is difficult to peel off all. Do you know any good idea to peel off old coating?

After peeling off some coating with a plastic ruler, I coated paraloid b72. It's more beautiful than before

What proportions of paraloid and acetone do you recommend to make a thin layer that gives consistency to the damaged side of the fossil? (it is broken, it is missing pieces of fossil, the side that is covered is healthy) so I put a layer on it to give it hardness on one side, so I can work on it without fear of it breaking.

What proportions of paraloid and acetone do you recommend to make a thin layer that gives consistency to the damaged side of the fossil? (it is broken, it is missing pieces of fossil, the side that is covered is healthy) so I put a layer on it to give it hardness on one side, so I can work on it without fear of it breaking.

Most Ammolite has an epoxy coating on it. Ammolite is just the marketing name for colorful ammonite shell. It is very fragile, hence the epoxy resin. There's no good way to dissolve it. The safest plan of attack is to cut your losses and leave it alone. You could try an application of Paraloid to the areas where the resin is gone just to bring some of the color back but that's unlikely. The iridescent part of the shell is in the top layers and usually comes off with the resin.

This partial ammonite whorl was a surface find from my April 8th trip to Cleveland, Utah. In particular, it was the one I found under the foot of the guy I was helping to lift his large Ammonite embedded in a heavy concretion to carry it to his van. I could discern that it was chocolate brown underneath the calcite coating. I stuck some thick felt furniture leg pads on the back of it to keep from scratching my office desktop. Well a week later I decided to remove the coating. Here's the "as found" pic. And with safety equipment including a gas filter mask, gloves, glasses, big bowl of water, a fan and open garage door, I was ready to go at it. The chemical is muriatic acid for cleaning brickwork and swimming pool masonry. I used a toothbrush to dip into a small cup of acid next to the bowl of water. Dip, scrub, rinse repeat until I liked the results. First round on this section. Looks good. Second round. Keep going! I'm liking it so far. Round three finishes that step. Then I soaked it in a bowl of water and baking soda. Several rinse cycles, a good dry time and a coat of Paraloid after that. Then the felt pads were reattached. And I like it a lot more than before. It may only be a partial whorl of an ammonite but to me it's a lot more than that. Kinda like finding a toe claw of a raptor or a big carnivore tooth. It may not be the whole enchilada...but it's enough to think about the potential of what it was complete or once was alive.

Looking good @Pagurus I have to echo the Paraloid comments. It will do a lot to stabilize the flaky little buggers. a 2% solution will lock the fish down without getting too thick on the specimen with additional applications if needed. I also get upset when bits come off. I've had some look great and then disintegrate before my eyes.

It’s pretty cool. The fins are flaky on all the fish and the Priksy and Diplo have flaky scales, but nothing patience and Paraloid can’t handle.