Paraloid B-72 | Hacker News Reader

Paraloid B-72

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286 pointsAriarule64 comments

Oh I've used this personally! I had various surgeries that removed various amounts of bone from me and I asked to keep the bones, which they allowed! I wanted to preserve them in case I wanted to make some esoteric jewelry and it lead to paraloid B-72.

It's quite wonderful. I dissolve the paraloid B-72 in acetone (1 part B-72, 8 parts acetone), then soak the bone in the acetone for about an hour, let the bones dry, and then suddenly they're solid and strong. You can adjust how much acetone you use for how thin/thick you want the fluid. Bones are porus so I opted for a thinner solution and it worked great. It was also really cheap.

Can we see the bones, Mr./Mrs. Bones?

Sure, here are some photos https://imgur.com/a/iPDdmDP

Hmm, what, the acetone evaporates and leaves just the plastic? Is that how it works?

And typically penetrates into the material (https://rhadhesives.com/why-chose-solvent-based-adhesives/).

Adhesives are a deep and interesting subject if you're looking for a wikipedia hole. For example, if you want the best general-purpose consumer structural adhesive, it's Loctite PL Premium MAX. For the best general-purpose consumer structural adhesive applied in wide temperature ranges, it's Liquid Nails Fuze-It MAX. If you want the best flexible general-purpose consumer structural adhesive, it's Gorilla Heavy Duty Construction Adhesive. For the best all-purpose consumer structural adhesive when properly prepared, applied and cured, it's epoxy resin. For the strongest general-purpose adhesive when tightly fitted and clamped between two porous materials, it's cross-linked PVA (wood glue). There are dozens of variables that change which adhesive is better per application.

>Adhesives are a deep and interesting subject.

It's notable that adhesives are something that Chinese manufacturers still really struggle with. Companies like Henkel and 3M have a deep reservoir of trade secrets.

> 3M

Since it hasn’t been mentioned in this thread: 3M 94 primer with 3M VHB tape is truly amazing stuff for bonding things with high surface energy.

high surface energy?

mahm/father I yearn for the spicy surface

They seem to have figured out some general purpose ones like B-7000 though. But yeah, agree on specialty stuff.

Yeah, the great part is you can then use fresh acetone to dissolve it. We do it with fossils all the time: glue it together, thin coat of glue all over then wrap and transport. Comes off easy in the lab.

Heh, I upvoted this a few days ago and it must've gotten on the second-chance queue.

Links to obsure but interesting Wikipedia articles are some of my favorite HN posts.

This is one of my favorite ones, just because of how crazy of an idea it was, as well as the fact it was deemed possible to build

https://en.wikipedia.org/wiki/Lockheed_CL-1201

Looking at that just screamed "coolest GI Joe vehicle that one rich kid at your school had and never let you play with".

Could this be used to 3D print supports ? For now, the only thermoplastic I know of that can be used to this effect is HIPS in conjunction with d-limonene.

PVA also exists, solves in pure water.

This is the most esoteric post I've seen on HN in a while.

How many museum curators who need non-yellowing flexible thermoplastic are there on here?

This post has exactly zero relevance to my professional career or personal projects, and this is exactly the type of esoteric content I love about HN!

Oil painter here, this is news to me and if it doesn't dissolve in gamsol this is EXACTLY what I've been looking for for about 2 years.

I followed the link to flexographic ink, and now I'm wondering whether boutique fine art flexography could or should exist. Like lithography, but more plastic.

What's the application?

It is used to strengthen materials. For example if plaster has crumbled, or the paint on a canvas has become flakey, or wood rotten, Paraloid B-72 can be used to hold everything together. The issue is that generally it is not reversible. Therefore one should always look at varnishes that can easily be removed and reapplied, but sometimes only Paraloid can hold everything toghther.

I meant in regards to use with gamsol but thanks for the insight

Yes, but that esoteric nature is the charm of HN at its best.

This is unusual as posts go, but it's not totally unreasonable and even though I wouldn't have an immediate use, it's fascinating, leads to further exploration (like another commenter mentioning the inks) and knowledge gets filed away.

I try to remember posts like this when people are less positive about HN! :-)

I use paraloid all the time, a bit surprised to see it posted here but I’ll support it.

I'm new to it and having trouble finding guides:

- how do I apply it as a coating? I want it to be ~ 1/6" to 1/8" thick and as hard as possible

- will turpentine dissolve or soften it?

I found a couple:

https://resources.culturalheritage.org/osg-postprints/wp-con...

https://www.zoicpaleotech.com/pages/paraloid-b72-in-fossil-p...

acetone will dissolve it, dunno about turpentine.

I'm reading that turp does not dissolve it, which is ideal so I can mix paint on top of it.

It's a relatively soft plastic and I don't think you can realistically build a uniform, good-looking layer that's 1/8" thick, if that's what you mean. If you need that thickness, high hardness, and nice appearance, I think your best bet is just a sheet of glass or acrylic on top.

It can be used as protective varnish, but that would be a very thin layer, probably 0.1 mm or something like that.

Does it not level from gravity like other resins?

It's solvent-based, so it won't set well in thick layers and it will shrink significantly as the solvent evaporates. You can do thick layers with solvent-free thermoset resins such as epoxy, but epoxy will yellow over time.

Purchase as crystals and dissolve in acetone or ethanol to desired concentration. It will self level based concentration, allow to evaporate before applying next layer

Not many, but there are a few amateur and professional musicians here benefitting from better piano hammers made possible by Paraloid B-72!

Note: I thought this was about Polaroid, not Paraloid, at first!

They should make non-yellowing transparent phone cases out of this stuff.

The issue is that it does yellow but after 25 to 50 years. The challange is that it is very difficult to reverse.

On the restoration of my house I allow its use on very specific cases. It very useful for example in strengthening wood that has rotten. Sometimes Paraloid is the only thing that can be used, but it needs to be used with care.

You can see the research here : https://www.woodresearch.sk/wr/201104/07.pdf?utm_source=chat... and here https://www.researchgate.net/publication/400226168_Aging_Mec...

Agreed. My gf uses it regularly as she's a furniture restorer, finding the definition here it's a bit of a surprise, though. Great, unique material.

It does not turn yellow, Paraloid B66 does. B72 has a low Tg, 40°C, so it can soften and creep when warm

It does discolor over time. The point is that one should be thinking about the impact over centuries and not years. It needs to be used with care and other alternatives need to always be considered.

For a painting or building that has survived for half a millennium we need use methods that will preserve the object for another 500 years.

Too many times I hear people say we will just use Paraloid.

Didn't really know of the different 9(!) versions of it. Thanks for pointing it out.

As someone who repairs and collects old computers, it might be one more tool.

I'm especially curious about the high upvote count, considering the Wikipedia article as well as the substance in general is not that interesting IMHO.

The high number of upvotes is the same phenomenon as the comment chain full of people patting themselves on the back for enjoying estoteric content on HN. They didn't read it, they just like to imagine themselves as the sort of person who would read it. They probably have an apartment with a shelf full of curated tastefully selected novels that were purchased used for the proper patina and arranged just so, and then forgotten until it's time to subtly attract their guests attention to how clever they are. They probably have a couple Hemingway references they have memorized and bring out when the time is right.

You must be fun at parties.

Paleontologist and probably going to be doing pre-museum prep for some stuff here in the fall.

Although we're cheap so we usually use butvar (polyvinyl butyral).

I've done some DIY piano maintenance and I saw what was presumably this available to firm up the hammers. My piano needs them softened, though.

Yes it mentioned firming piano hammers in the article. From what I remember, a piano hammer is a shaped piece of wood (or several?) with a leather strip around the striker part? What is the difference for you between hardening and softening the hammer, and how would it be done with this .. is it penetrating? (acetone base would enable that, it is used for carrying chemicals through a surface). Could you soften the hammers by replacing the leather strips, or soaking them to loosen & expand the presumably compacted fibres?

In my wider life in the UK, speaking to people associated with pianos (from a piano tuner, to school premises teams), it is often not worth the commercial expense to repair old pianos unless they are of particularly good quality or have some sentimental value.

The hammer is felt around wood. You don't replace the felt, you'd replace the entire hammer, but then you'd likely want to replace all the hammers to get matching sound anyway.

There's a solution you can add to soften the hammers, but I don't know what chemical it is or how well it works since I haven't tried it yet; you can also needle the felt to fluff it up.

Huh. So it's a stronger, harder, less brittle, clear wood glue you can dissolve with acetone. Neat!

How does its strength compare to MMA structural adhesives? What materials is it compatible with?

My only expansion for MMA is “mixed martial arts” and I’m not particularly familiar with it. Maybe there’s a wrestling move called the “structural adhesive”?

methmethacrylate (ie acrylic)

Methyl methacrylate*

polymethylmethacrylate (PMMA) is used extensively in photolithography of silicon chips.

More posts please relating to conservator tech or websites. Thanks.

Would this work for fragile shells and things like sand dollar “skeletons”? I usually use thinned white glue, but it’s less than ideal.

Yes this is exactly what we use it for.

What we really need is a wipe on self leveling version. Finishing guitars is hard!

Am I the only one that read it as Polaroid ;) ?

I thought it was going to be about a bomber with a parabolic-shaped wing, or something similar.

I read it as "paraboloid" and expected it to be about some very specific geometrical shape with a niche practical application.

No,you are not. I was expecting it to be a camera.

I thought it was a cross between a camera and a bomber.

Edwin Land, the inventor of the Polaroid, worked on the U2's camera.

https://otislibrarynorwich.org/2024/04/08/edwin-land-and-the...

https://www.smithsonianmag.com/innovation/polaroid-inventor-...

Polaroid for B-72 bomber

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