I want to give a turned bowl to someone as a gift, but I know they will inevitably use these bowls in the microwave.
From my own experience of force-drying wood in the microwave, I know it can get hot to the touch after about 30 seconds, depending on moisture level.
Are there any finish solutions for making "microwave-safe" wood items for serving food on?
Are there any finish solutions for making "microwave-safe" wood items for serving food on?
It's not so much a question of "microwave-safe" finishes as "microwave-safe" materials.
Microwaves work by exciting water molecules, thereby increasing their energy (i.e., heating them up). The reason your wooden bowl gets hot is because of the water trapped in the wood fibers.
I would strongly advise against microwaving a finished wood bowl for not only the risk of burning oneself on it, but also because the rapid heating of the water in the bowl can cause it to crack.
I want to give a turned bowl to someone as a gift, but I know they will inevitably use these bowls in the microwave.
Very clearly tell the intended recipient that wooden bowls are not microwave safe. If someone uses the bowl improperly and it breaks, yes, that sucks for them, but you're not at fault having told them. Common sense has to factor into things sometimes.
By the way, not only would I tell them to not microwave the bowl, but don't soak it in water, and don't put it through the dishwasher either.
If the wood in the bowl is dry it won't heat up and it won't crack Even "dry" wood has moisture in it. It's near impossible to remove all moisture from a piece of wood. Eating hot food isn't really an issue because you're not turning the entrained water in the bowl to steam like you would with a microwave.
I would seriously suggest you just get them a glass or plastic bowl if you want to gift them one you know they'll want to use in a microwave :-)
Regular microwaving is not a good environment for wood since it'll heat it and drive out moisture. Up to a point this doesn't do any harm as you'll have some idea about from your force-drying experience, but if you've ever overdone the microwaving as I have (causing the water in the wood to boil) you'll know there are some issues.
First thing I'll mention is the one that will be most immediately apparent: the smell. If they do overheat the bowl even just once and it boils the intrinsic water they'll create wood steam and the smell of this is not exactly conducive to fine dining (think paper mill and you'll have some idea)! Worst still, that odour will linger in the microwave for months. Trust me that's no exaggeration, I speak from experience.
In terms of the safety of the bowl, past a certain level and the wood will end up way dryer than is natural. With repeat use the moisture level will cycle up and down excessively (most especially if they wash it). I think you could bet money on this leading to warping or cracking, even if the wood used in the turning was straight-grained and clear.
More seriously given enough microwave exposure there's even a risk of fire. If the wood happened to be very dry already, from being microwaved recently and/or because of local conditions, and it was then microwaved for a good amount of time you could get localised scorching. And once the wood is charred it's just a small step to ignition (same basic principle as char cloth).
While you can often get away with wood in a microwave you shouldn't. Or if you do, mass-produced cheap things but not something presumably valued. Similarly for the dishwasher - I put some wooden things in there but nothing that couldn't be replaced cheaply and easily.
But to be honest, finished wood and hot wet foods don't mix well, so using it in the microwave would be rather pointless (except I suppose for warming bread).
Varnishes tend to crack or peel while oils (even food safe ones) can give a taste to the food.
I have stained my cutting boards and place hot pizza pans on them with no effect. However they still will warp with constant water left on them.
I would suggest you have two options. Rubbing mineral spirits or butchers block oil and finish with cheesecloth or tack cloth.
When in doubt test on the wood in question. Stain a scrap of wood then buy a cheap heat gun. Use the heat gun for a prolonged amount of time to see its affects. This will prevent any damages to actual equipment tests. It will also assure you of your friends sanity.
On food contacted stains I like it to rest for a month if not weeks to make sure the stain completely soaks in.
Also make sure to take a plain cloth and wipe any access stain buildup. You usually do this after 24 hours of curing..
When creating wood products that will be used with food. Either dry, wet or microwaved the guidelines are generally the same for all the above.
The microwave doesn't change anything. The wood item will simply wear out quicker if it is microwaved. The point here is to keep it non-toxic and food safe. Microwaved, dishwasher or washed in the sink. You don't want to leach any poisons into the food as a result.
I make butcher blocks. They are easy to make and people love them as gifts. Here's what I follow as guidelines.
Some of my blocks are over 5 years old and still safe to use.
