Comment by throwup238 | Hacker News Reader

Comment by throwup238 | Hacker News Reader

> These days, some hobbyists opt for modern epoxy instead of the traditional and expensive Urushi lacquer. Epoxy probably yields a more robust bond and certainly allows for quicker repairs, but I question its safety for food-related use, especially at the temperatures found in a steaming cup of coffee.

People opt for epoxy because Urushi lacquer is traditionally made from poison oak sap and is a potent skin irritant to most people (it's where urushiol gets its name). It's really tough to do Kintsugi without smearing trace amounts of it all over the place, especially if you're doing it with kids, and cleaning it off is a pain since it's a hydrophobic sap. Even trace amounts can cause a reaction, especially if someone has sensitive skin or is severely allergic. People who do a lot of kintsugi develop a tolerance for it but it's an annoyance that most hobbyists just don't need.

Epoxies can be perfectly food safe and the FDA has a database [1] although it's not particularly user friendly. You can get MAX CLR or similar from Amazon. I wouldn't use it in an oven above 300F but it's fine for boiling temps. These FDA approved two part epoxies are used all over the place in hospitals and food manufacturing facilities where they're used to coat rough surfaces that would otherwise harbor bacteria.

[1] https://www.cfsanappsexternal.fda.gov/scripts/fdcc/?set=Indi...

I spent a few years messing with different approaches with epoxy but I never found anything that could replace urushi. It's really hard to get foodsafe epoxy to cure as hard as urushi, though I did eventually get one I was happy with. But the wheat flour in the traditional material pulls the shards together as it dries, and gives just an incredibly tight and strong bond that can really hold up to actual use of the restored vessel. Epoxy always weakens and fails after a while, while I have urushi/wheat/clay pieces that have been in daily use for years.

Depending on your goals though non-foodsafe epoxy can work well. Thickened marine epoxy, for under-the-waterline boat repairs is rock solid for decorative items. I'm sure it's toxic af and I wouldn't want it anywhere near my food but it would be fine for a lot of the things people want to do kintsugi for.

Cashew lacquer is also pretty cool. It's nowhere near as nasty as urushi and doesn't require a special environment for curing. If I were just getting into it now I'd probably start with that.

> Cashew lacquer

Hum... That can't be a coincidence. Both plants are on the same family. Let me check...

Yup, Cashew produces urushiol also. Unlike pistachos, cashew shells must be removed before selling the fruits for this reason.

So cashew plants can trigger skin allergies. Is a common family thing. Harvesting this things burn the workers hands. My bet is that would be also unsafe for people allergic to poison ivy.

Weirdly enough, the food safety of urushiol was the topic of this recent and heavily discussed HN post: https://news.ycombinator.com/item?id=40399224

I can't say I have any desire to try it myself.

I'm not a doctor/chemist, but as far as I understand, the polymerization of urushiol renders it hard and inert. Your thread discusses contact with raw urushiol as found in poison ivy, cashew sap (and apparently mangos) which is indeed known to cause allergic rashes in most humans. I'm not saying that kintsugi is definitely food-safe, but it's an important distinction.

Side-note: I did get some raw urushi on my fingers while working on this project, but nothing happened. Perhaps I'm immune.

> Side-note: I did get some raw urushi on my fingers while working on this project, but nothing happened. Perhaps I'm immune.

Might also be enough mechanical rubbing on fingertips during normal use that it mostly scrubs off. Whenever I feel it coming on from Urushi or accidentally touching poison ivy in nature, I rub it with water and course sand/dirt which seems to get rid of the urushiol.

How do you “feel it coming on”? Would love to develop a sense for it so I can save myself from days of discomfort.

I have sensitive skin so I start to itch shortly after contact and it builds from there. If I get it scrubbed off fast enough after exposure, I can usually prevent full contact dermatitis from setting in.

Urushi is more of a pain in the ass because its made from the sap, but Windsor and Newton artguard barrier cream seems to really help. Ideally apply it before use but it helps washing it off too if you forget.

Tecnu seems to help quite a bit in my experience.

A lot of people seem immune the first time. My mom thought she was immune to poison ivy, but after years of contact she became increasingly sensitized. Now she gets a rash of the cat has been walking through it.

> Side-note: I did get some raw urushi on my fingers while working on this project, but nothing happened. Perhaps I'm immune.

Somewhat the opposite. To be immune to it, your immune system would likely have to tolerate the authentication failure this substance causes after binding to a cell…which could be Bad in many other ways.

A likely explanation is that you removed the substance before an immune response could be mounted.

Molecules of the contaminant bind to skin cells around 15 minutes after contact. The affected cells are disrupted only in that they can no longer provide the appropriate response when challenged by an immune cell. When a cell cannot be identified as a member of the host, a chemical signal is released which tells killer immune cells to congregate and kill everything in the area.

This attack mounted by the immune system is the source of the irritation. It can be mitigated by antihistamine (somewhat), lower temperatures (somewhat, espeically on the verge of shivering), steroid injection (strongly).

Note that recontamination is the most common cause of "spread". Only a single molecule is enough to cause a reaction. Contaminated clothing and surfaces can still bear the oil after multiple washings.

I've never trusted that food safe epoxy actually is. I'm afraid that lobbyists have interfered, or its a situation where "there's no evidence that it's dangerous but there's not really evidence that it's safe", or the studies are funded by manufacturers, or there's something like manufactures pulled with BPA where they just switch to something functionally equivalent to a potentially dangerous chemical.

Is there any reason to believe that these epoxies won't just be like PFAS where in a few years the EPA/FDA will decide that they were actually risky?

I’m with you. I assume all plastics to be unsafe for human use by default.

It's confusing. There's food grade and food safe. There's some more information here, and it's still confusing.

https://www.wisebond.com/blogs/epoxy-blog/is-epoxy-food-safe

I’m always worried about food-safety and Amazon. They don’t have very good control over their inventory, right?

You can even get (tobacco) smoking pipes decorated using urushi. It's made me wonder about the temperature stability, as a pipe can (but ideally shouldn't) get fairly hot.

Tsuge is a good brand to search for if you want to see exanples. Cost-wise such pipes start around the two hundred US mark.

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