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A Quick Guide to Paraloid-B72 (with mixture ratio)

Discussion in 'Skulls and Skeletons' started by DancingCoyote, Oct 6, 2017.

  1. DancingCoyote

    DancingCoyote Member

    I posted this in a reply to someone a while ago but figured it'd be worth a post of its own.
    I've seen many very loose ideas of paraloid/solvent mixtures but nothing too precise. A while back I sat down, did experiments, and measured to find a good starting point for mixing paraloid so others have a better idea of where to begin their mixture.

    Thin Mixture Ratio:
    4.3% Paraloid to 95.7% Solvent is equal to 1 & 1/2 teaspoons Paraloid to 1 cup Solvent is equal to 2 grams Paraloid to 159 grams Solvent
    This ratio is very thin so it soaks deep into the bone and leaves no to minimal gloss. You may still have slight gloss on the underside of the skull due to gravity affecting the mixture.

    If you find this recipe to be too thin for your liking and you want a heavier/glossier coat, add 1/2 teaspoons to 1 full teaspoon of Paraloid to the mixture at a time, testing in between, until you get your desired thickness.

    Quick FAQ:
    How much is Paraloid-B72 usually?
    The current going rate seems to be about $25-$30 for 1 pound. If you're a hobbyist, this will last you a long time. You can find the pellets for sale on a few museum/conservation and art supply sites (google Paraloid-B72). Sometimes the stuff pops up on etsy and ebay.

    What solvent do I use?
    Acetone. Denatured Alcohol can also be used supposedly, though I haven't tried it.

    How do I make the mixture?
    Figure out how much you want to make and then measure out your ingredients. You'll need to do a little math. For example, if I want a little over a half gallon of mixture and want to measure it out in cooking measurements then I do this: 1 half gallon is equal to 8 cups. Therefore, I need 8 cups of solvent. For the paraloid part, 1 & 1/2 (or 1.5) x 8 = 12 teaspoons of paraloid to 8 cups solvent
    Put your solvent in first and then slowly sprinkle in your paraloid pellets. Try not to just throw them all in the same spot because they'll stick together, making it take longer to dissolve. Stir the mixture every so often.
    Big tubs of thick mixture may need to be made 1 or 2 days ahead of time. Small, thin mixtures only need a couple hours, if that.

    Is the mixture reusable? What if the solvent evaporates?
    Paraloid mixtures are infinitely reusable as long as your tub and skulls are clean. If your solvent evaporates, just add more solvent to redissolve the paraloid.

    Where should I store the mixture?
    Always keep a tight lid on the tub. If using acetone, keep large tubs of it away from things like heat and open flame. Very tiny bowls of it will be fine to keep in the house (not much different from a bottle of nail polish remover), but use common sense and follow the precautions on your solvent's container. Again- keep it covered and away from heat/flame.

    How do I test the mixture?
    Stir the mixture well. Dip your fingers/a popsicle stick/whatever into the mix and fling a drop onto a plastic surface. Wait about 5-10 minutes. Peel the drop up and check the thickness.

    What container do I make the mixture in?
    Either glass or plastic tubs that have #2 on the bottom. The glass mixing/left over bowls with tight rubber lids that you can find at walmart/target are great for tiny specimens and brushing the mixture, but you can find the large plastic tubs with #2 usually in hardware places like Home Depot and maybe Walmart if you want to dunk larger skulls.

    How long do I soak?
    Varies from person to person and how dense the bone is. I work primarily with small to medium animals so I soak for 3 to 5 minutes. As long as the mixture is covered, soaking the skull for longer shouldn't hurt anything.

    Can I just dive right in with a freshly-cleaned skull?
    I wouldn't advise it. Due to how annoying it is to remove paraloid, you'll ideally want a waiting period before you seal it. Degrease well, wait about 5 months to a year after degreasing to make sure no deep grease you missed is coming to the surface. Very small animals that have next to no grease (like squirrels, I guess) may not need much, if any waiting time. Use your own judgement with the individual skull. Due to the waiting time Paraloid is usually better suited for museum stuff or personal skulls.

    What if my animal is too big to soak?
    Get a paint brush, dunk it in the mixture, and apply it to the skull. Do not load up your brush. Try to brush it on fast and spread it as thin as you can. Work in sections. If you make gloss spots don't worry, you can buff them down later.

    How long does it take to dry?
    Depends on how thick the mixture is. This very thin base ratio dries a lot longer (about 15-20 minutes) due to the higher solvent content. The more paraloid you add, the less drying time there is.

    There's some solid plastic drips on the skull, what do I do?
    Take a scalpel and cut off the excess. Take a microfiber cloth with straight solvent and buff down any remaining excess paraloid in the spot.

    I want a natural bone look but there's some gloss spots, what now?
    Easy fix. Take a microfiber cloth (you can find them in eyeglass stores) and put straight solvent on it. Buff the gloss down.
    The cloth will start to take on paraloid. To reuse the cloth, soak it in straight solvent for a few minutes and wring it out before using again.

    I want a glossy look, what do I do?
    Either make your mixture thicker with paraloid and/or do multiple 2-second dunks after the initial soak until you get what you want. Allow the skull to dry between each dunk.

    How does Paraloid compare to a cheap spray sealant or mod podge/elmers glue?
    Paraloid is far superior in most cases. Though much cheaper, modpodge and Elmers tends to get tacky with handling over time (causing dust to stick to the skull) and aren't moisture resistant. Various clear sprays are a fine middle ground, if not the best option if you've painted the skull. Paraloid is more final (while it *can* be removed, it's a bit of a headache), so you must be sure all grease is out of the skull before use, but it will strengthen the integrity of the bone much more than other mentioned sealers as well as help protect the skull from frequent handling (ideal for classroom skulls) and moisture/temperature change.
  2. Sea Wolf

    Sea Wolf Well-Known Member

    Good post and helpful. Denatured alcohol can indeed be used as a solvent. The resulting solution will be milky colored. The end result is the same as with acetone. The drying time will be a little longer and the alcohol is actually less volatile (and safer/cheaper) than acetone.

  3. Sea Wolf

    Sea Wolf Well-Known Member

    As a note, if the skulls appear grease free, they can be sealed right away. I normally seal skulls as soon as they are dry from whitening. If oils show up later, it is an easy task to drop them into acetone and let them soak to thin and remove the paraloid. It also sets them up to continue to soak in acetone to remove the grease or go to ammonia or detergents again. I guarantee my skulls and will take back any that show grease later and correct it. So far, no returns.
  4. DeerMan43

    DeerMan43 Member

    Thank you for posting this very useful post. I’m going to give this a try here sometime.
  5. Great Post. Thank you for your time.
  6. Erin Walker

    Erin Walker New Member

    I'm trying to preserve an old, crumbly bull skull. I'm not sure what to use to soak it as it it's fairly large - with horns, it may be a couple feet wide. The trouble is the horns are the most delicate part, so I have to be careful with the size of the container. I'm planning on using denatured alcohol. How many gallons would you recommend I need? And would a half-pound of paraloid be enough? Or a pound?
  7. Sea Wolf

    Sea Wolf Well-Known Member

    Can you find some sort of plastic container/tub that the skull will fit into, horns down? Possibly that or on it;s side? If so, you would be able to soak it by soaking one section at a time, flip it over and do the other side. For that, without seeing the container, I would do 2 gallons. You can also tip the container on one end or the other at an angle to make the solution deeper on one end and submerge more of it. I would probably shoot for a pound as you will use a little more adjusting the thickness of the solution after it is made up. There is no waste with it. After you are done, You can allow the alcohol to evaporate down and recover the resin and put it back in a container to use again.