Kuksa advice

[Margaret]

I bought a Kuksa from an independent Swedish seller (it was quite expensive) - I loved it and used it constantly lately, but then it developed a crack along one edge. I can't think why as I followed all the instructions. All I did that was "different" was to give it a sanding with a very fine sandpaper to smooth it as it was a little rough. Now I've bought a new, also quite expensive one via Amazon, from Nordic_art_store, advertised as from curly birch. I want to do what I can to avoid this one getting a crack too. I have also sanded it very lightly, but was that a mistake? Do I need to do something to the surfaces I sanded?

I read something about the growth rings on here, but I can't really judge as they vary. Mine are quite wide (near 1cm) in places. Any advice most welcome, I'd like this one to last and not to have to buy another, funds aren't endless ;-)

 

[crosslandkelly]

Keep it well oiled, I use tung oil or walnut oil.
Here are some tips.

"Hand wash and dry it before initial use.
Oil Regularly: Dry wood has a tendency to crack, so keep you Kuksa oiled up to avoid this.
No extreme temperatures: Give your boiling liquids a few minutes to cool down before pouring it into your Kuksa. Also avoid microwaves and dishwashers."

 

[TLM]

Well..... the way to make it almost totally split proof (from moisture induced strain) is to leach all resinous substances out with acetone or comparable solvent and then vacuum impregnate it with some oil that preferably polymerizes into the wood (like cobalt catalyzed linen oil). I admit that it is a slightly heavy procedure. An additional help would be a treatment to get rid of glycidyl groups in there, several possibilities.

Some manufacturers of kuksas impregnate them with salt water, salt tends to keep it moist and non splitting. Some use paraffin oil for treatment but that does slowly come out if used with hot drinks. One way to keep it slightly moist is to use it every day.

As CLK said, no microwaves or dishwashers.

 

[Margaret]

Thanks all - is there a particular reason for using Tung/Walnut? I don't have those, I do have olive oil and argan oil - I've just given it an oiling with the argan. Generally I've been pouring hot water from a flask but maybe I should leave the kettle a few moments before pouring into the flask. It could be that I poured directly from the kettle into the previous, now cracked kuksa a few times, can't remember. TLM, I've gotten into the habit of using it all the time lately as I like it so much over conventional mugs - I don't think i'm going to try those anti crack methods, although they do sound interesting.

 

[C_Claycomb]

Problem with kuksa

Dear Fellows, I've bought a kuksa several years ago. i used it seldom because everytime the wood releases an greasy patina, probably due to the oil used for the cup by the maker. I attempted several uses, but even with water it seems impossible to drink without a brothy aftertaste Any idea how...

bushcraftuk.com

https://www.reddit.com/r/woodworking/comments/e7p5x0

Short version is that things like olive oil (many veg and nut oils) can go rancid, and they do not cure, so are free to leach out of the cup when warm liquid is added.

Tung oil cures hard by an oxidation process. I have used it on spoons, following Robson Valley's recommendation to heat the spoon first in the oven to expand the air in it and allow oil to be drawn in as the wood cools. It takes time, but seems to work well.

 

[Broch]

And I use a light wipe of whatever vegetable oil I have to hand each time I get home. I think, for stuff that's used regularly, it's fine; I have never had a utensil that I use go rancid. The very fact that it gets leached out and is then replaced with fresh may be why it can work. The only time I have experienced utensils crack is when they have been left soaking in the washing up water (by others I should add).

It just goes to show that peoples' experience varies though I appreciate you don't want to 'experiment' with something of value.

Welcome to the forum BTW

 

[TLM]

I don't think i'm going to try those anti crack methods, although they do sound interesting.

They first are not the most practical but the salt water treatment is. I have seen a set of coffee cups made from birch during WW2 for Field Marshal Mannerheim, about 3mm thick, when asked the guide said that "they were treated with salt" I don't know if wet or dry but there wasn't any cracks in the set.

 

[punkrockcaveman]

The timing of this thread is unbelievable. Last night I finished turning this birch cup (my first ever cup, my first ever use of a gouge chisel thingy and my first real project on the lathe!) I had a beer out of it to celebrate



So it needs treating and I was going to use veg oil however, I like this salt idea and I'm well up for sacrificing it for the sake of experimenting. I can always knock another up

 

[TLM]

There is some history for the heavier chemical treatment, I got that from a prof. emeritus of wood chemistry in University of Helsinki when I happened to ask him.

 

[Broch]

Sorry TLM but I cannot recommend the treatment of wood with salt by anyone that does not have both the facilities and experience to do it; there is a real danger that it will cause more damage than good. It really needs to be applied under pressure to ensure the salt actually impregnates the wood instead of just sucking all the moisture out from the surface. If you know of a reliable 'kitchen table' method I'd be pleased to hear of it

 

[punkrockcaveman]

Ah I see. Maybe not the salt method then. I was thinking a layer of epoxy resin or two but I'd rather use oil if I can get away with it. Could you 'cook' the oil into the wood?

 

[Broch]

That's a very nice little cup. If you're only going to use it occasionally I would follow Chris' advice and use a curing oil on it. If you're going to use it every day - well you have more choice

How big is it; It's a lovely shape to drink a wee dram out of but maybe it's too big for that?

 

[TLM]

just sucking all the moisture out from the surface.

With very fine dry salt that might happen, no chance if supersaturated water solution is used. Even with dry salt if the wood is very wet the water there will just dissolve the salt. It could take some time for the salt to fully impregnate the wood, diffusion takes time. For pressure to work one would need very dry wood, better to use vacuum with or without pressure.

 

[Broch]

Oh well, to each their own, I have only ever used salt to accelerate drying of wood (like salt cured fish) before oil soaking. And then, only on relatively thin sections otherwise I think the drying gradient would be too high and cause cracking. I have never tried to impregnate wood in a utensil with it to preserve it.

 

[TLM]

Silicagel beats salts for just drying things. For proper soaking I have used a vacuum chamber with a bath of the intended impregnating oil at the bottom and hung the wood above it. Used about 0.05 bar absolute or what ever the water injector happens to give. Give it an hour and then drop the wood into the oil so that it fully submerges and then turn off the pump and let it stay there for another hour. That gives a fairly repeatable result. Warming the surface and then coating is a trick carpenters use when they want to avoid bubbles in the clear lacquer, works well for the surface.

 

[bobnewboy]

I’ve had good results using eating-quality walnut oil, applied heavily while very hot to the room temp wooden item. I do this twice with a 24 hour gap between, leaving the item in sunlight (or daylight) and then wipe the wooden item down with a clean cloth or paper rag. Be careful with the hot oil though, it appears to have a high capacity for heat, so only use a heat resistant container. I heat mine for a short time in a ceramic mug in a microwave.

Walnut oil polymerises in sunlight, and I haven’t had any issues with spoiling at later dates.

 

[oldtimer]

Now I understand how I wrecked a turned wooden salad bowl by putting olive oil based dressing in it.

I like the aesthetic qualities of the kuksa but I'm glad I learned to make ceramic pots: so much easier to make and maintain. One can see why pottery caught on so early and continues to be used.

 

[crosslandkelly]

I understand that boiling a kuksa in milk will seal it. I've not tried this method though.

 

[Margaret]

And I use a light wipe of whatever vegetable oil I have to hand each time I get home. I think, for stuff that's used regularly, it's fine; I have never had a utensil that I use go rancid. The very fact that it gets leached out and is then replaced with fresh may be why it can work. The only time I have experienced utensils crack is when they have been left soaking in the washing up water (by others I should add).
Welcome to the forum BTW

Thanks - sounds like a sensible easy option I read up on Tung oil and hearing that it hardens somehow put me off, so I might try walnut oil. In the meantime the argan oil soaked in very nicely

 

[TLM]

that it hardens somehow put me off,

Hardening is actually a good thing in wood treating, there are less reactive sites where molds, oxygen etc. can attack the oil. Don't we have a resident organic chemist?