Developing a food-safe finish for my wooden spoons

Highly-refined mineral oil is food-safe.

https://en.wikipedia.org/wiki/Mineral_oil#Food_preparation

Why even use wood if you’re going to cover it in a layer of clear plastic?

I find it amusing that those who will use wood or "natural" (petroleum is also naturally occurring...) products for some sort of weird misguided eco-virtue-signaling, inevitably end up needing to basically reinvent the chemistry of finding an inert, durable material that brought us modern plastics. All these drying oils create a layer of polymerised material, which can be classed as plastic anyway. Waxes, regardless of source, attribute their properties to long hydrocarbon chains, just like polyethylene.

I find it bizarre that these finishes market the HDI component as an “accelerator”. It seems quite clearly to be a crosslinking agent — it’s a longish molecule with a rather reactive isocyanate group at either end. If you mix it with things it can react with, which likely includes both some waxes (those with hydroxyl groups) and some of the modified oils in “hardwax” oil, it will turn them into something akin to polyurethane.

Rubio Monocoat will cure into a different substance with the “accelerator” added than without it. In either case, it cures quite slowly and IMO has a nasty, penetrating chemical smell for weeks. I like how it looks, but the finish is not as stain resistant as many other options are, with or without the HDI.

P.S. the SDSes and some common sense suggest that this stuff is actually HDI oligomers, not plain HDI. The oligomers are rather less nasty.

P.P.S. Isocyanates are, AIUI, not persistently nasty, as they are too reactive. They react with water to form amines, and unreacted isocyanates will react with the amines to form polyurea, which is reasonably inert.

P.P.P.S. The “molecular bonding” stuff that Rubio talks about seems to be nonsense. The part A + part B mix will cure into a fairly hard and tough plasticky substance even if it’s a millimeter or two thick. Don’t do that — it’s not so easy to get the resulting mess off of whatever surface it cured on!

This is very confused.

First, all wood finishes you can buy are food-safe once cured. They aren't allowed to be sold otherwise, at least in the US/Europe/et al.

If you are using them once heated, this is not always as true (and regulations vary a bit), but if we are talking about food prep/salad/you name it, they are all safe.

Heat wise, if we are talking about using it in boiling water to stir something, most finishes would be fine from a safety standpoint (not all can withstand this though).

As a general rule of thumb, if you aren't heating the wood above 200F, you aren't really going to get a finishes to release toxic fumes[1]

Second, as for solvents - smell is not everything. The HDI he mentions rubio having will not smell like anything until the concentration is way way way way too high. If you can smell it, you are in trouble. HDI is also much more dangerous than most solvents[2].

The oil is also a solvent.

Solvents are just things that you can dissolve something else in.

If they want to avoid certain types of solvents for some reason, that should be about safety or something, and if they want to evaluate that, smell is probably the wrong evaluation criteria.

To give one example of solvent elimination with a purpose, let's take VOC's, which are about pollution[3].

Avoiding VOC solvents makes for cleaner air, but again, VOC compliant/exempt/etc solvents vary wildly in whether they are safer for people or not than non-VOC exempt solvents.

If you are trying instead to avoid human-toxic solvents, you would choose a different set, etc.

[1] There are so many finishes with so many different properties that i can't 100% guarantee this, but non-professional stuff you can buy at a woodworking store or a big box store is going to be fine

[2] The lack of smell of isocyanate's is main the reason you can get service life indicating respirator catridges from 3m/et al - otherwise you would not be able to determine if your cartridge is working or not, since you would not smell it when spray finishing/etc until the concentration is way too high, even if your cartridge is spent. Sane folks just use supplied air anyway, rather than risk it at all.

[3] not safety to humans, though often highly confused with being safer.

And the reason is exactly the finish. Metal and plastic spoons, forks, lids, etc. are nice and smooth and don't get in your way. Cheaply made wood or cardboards ones are rough and tacky.

Of course you could argue that from an environmental standpoint, that's not a bug but a feature: now I'm using even less disposable stuff (first, no plastic because it's been replaced by other stuff; and second also the replacements because I hate using them).

https://www.finewoodworking.com/2024/10/10/the-best-food-saf...

Urushi is the name of the Japanese tree, Toxicodendron verniciflua (the genus formerly was named Rhus), and of the lacquer of which its sap is the main constituent.

The lacquer is also called urushiol (note, not urushoil), which is also the resinous substance found in other members of the Toxicodendron genus: T. radicans and T. rydbergii, or poison ivy; T. diversilobum and T. pubescens, poison oak; and T. vernix, poison sumac. The resinous oil is what causes allergic reactions.

Which finally gets to my point: What are the allergic affects of the tree, its raw sap, the liquid lacquer, and maybe for hypersenstive/reactive urushiol allergies, the finished lacquer?

I don't meant to be alarmist - people have been eating off urushi lacquer for centuries. I'm thinking more about working with it.

EDIT: For those interested in the scientific aspects of the resin, plants, and allergic reaction:

Aaron C. Gladman MD. Toxicodendron Dermatitis: Poison Ivy, Oak, and Sumac. Wilderness & Environmental Medicine vol 17 #2 (June 2006)

https://journals.sagepub.com/doi/10.1580/pr31-05.1

I throw it in a bag and vacuum seal the spoon (with tung oil) for a day or two, then remove, wipe, and let cure for a month.

The resulting finish is largely dishwasher safe for a year or so before I have to reapply. Without the vacuum sealing stage, it doesn’t last as long.

Even for hobby work it’s not hard to get reasonable VOC protective gear or establish a fume extraction hood out of some cardboard and a cheap box fan next to a window in the shop space.

It's still a combination of polymerizing oils, hard waxes and resin, it's just different plants (linseed instead of tung, pine resin instead of damar etc.) Again, no solvents, people say it smells good.

I still have way too much tung oil, wax and resin around because I could only buy high quantities, so I guess I'll keep using my own finish for a long while. But I'd love to hear from others how the Furniture Butter fares for wooden spoons and cups.

Couple of years back I went to all wooden spoons in the kitchen. My all time favourite is the most traditional of all: boxwood. This is what wooden utensils are made in my home country for centuries. It's light but dense, hard, and durable. It doesn't absorb color or smells easily as other hardwood. Beautiful too!

Of course, the article is about high end stuff, but I just want to put everything in the dishwasher. Which I presume you can't do with even the best coated high end utensils?

We also switched to wooden Cutting boards, I find them to be pretty annoying as they really go bad fast in the dishwasher and can be quite expensive. We just wash them with boiling water, a bit of soap every now and then.

Generally I use a beeswax and mineral oil finish, sometimes this other product I can't remember the name of made from flax oil.

I've been wondering why jojoba oil doesn't get mentioned more in these discussions, either in combination with something else or on its own? It's a wax but liquid at room temperature, and seems to be stable for a long long time, long enough at least that it would probably need some refinishing before it might go bad.

Your shop looks great too. Others might enjoy folowing the link buried towards the bottom of the article.

Wood is great for serving spoons, I have some fancy French ones, you just never dishwash and every few months wipe down with grapeseed or canola oil.

For eating? Wood just is not a good material.

   But it’s really hard to mix properly and apply on small wooden objects like spoons and cups. I almost always use too much accelerator,

Burnishing for spatulas for example can be done on a drill press. Just use a smooth rounded end steel bar and a low speed on the drill. You’ll have the concave part done in minutes. For the handle and convex part it’s usually easiest to burnish with a smooth steel rod and move the piece along the side. I can get my hard maple spatula burnished in under 15 minutes.

If you really want to keep the fibers from rising a lot post burnishing- water pop the wood, sand with 220, slightly dampen the wood again and then burnish.

I haven’t tried this but apparently you can automate the burnishing by using antlers/smooth stones in a rock tumbler.

Works well for me

For the exterior and for cutting boards, I use a hard wax oil I make from linseed oil and beeswax. It's easy to prepare and I usually provide a small cup of it to whomever I'm gifting the cutting board.

I reuse small, glass jelly jars with screw-on metal lids, about 1/2 a cup in size. You do need to leave a layer of water on top, though, because otherwise the top layer will polymerize and leave a rubbery layer you have to remove the next time you use it.

To head off the people who will jump up-and-down calling me paranoid for not considering untreated printed works food safe, and accusing me of accusing them of poisoning family & friends (in some circles the discussion can get more cantankerous than the vi/emacs thing!): you keep using printed things for food without treatment if you like, and I won't judge, but I prefer to remain paranoid because if printed items were food safe it would be a selling point and I don't see any manufacturers using food based examples in their advertising.