Mineral oil will not go rancid over time… It will not dry (or cure) either. Mineral oil is a non-drying oil and as such, it will continue to leech out of the wood when it's washed. If you apply too much, it weeps it's way through the board/bowl etc, leaving a nice greasy ring on your counter, or on your Mums Irish lace tablecloth (don't ask). It is considered food safe and a version of it is sold in drug stores for intestinal disorders.
Walnut oil does indeed taste better than Mineral oil… I cook with Walnut oil (from the grocery store) all the time. In fact, it's about the only oil I use in baked goods anymore. I prefer Walnut oil for Treenware (utility wooden objects like bowls, platters, cutting boards etc) because it's made from edible nuts. Mineral oil is made from petroleum. If I have to eat one, I choose Walnut oil! ;-)
In my studio, I have numerous clients who are concerned about finishes that may have contained toxic ingredients (as they define them). Still more that have asthma and other respiratory ailments that make them sensitive to fumes, or are extra concerned about anything they have in their homes.
To address these concerns, I offer a line of what I call "sensitive" finishes, for those clients who prefer a more natural finish on their woodenware. These include pure Beeswax, Walnut oil and Shellac thinned with a drinkable (from the local liquor store) alcohol, along with a few other exotic food based oils.
Whenever this subject comes up in woodturning circles there are always responses like: "All finishes when cured are food safe"... and similar comments. While that may or may not be true, it is irrelevant in the grand scheme of things. Why, because the client's opinion is the ONLY one that matters… Period. It's their money and their life, so they get to make the decision. I can talk till I'm blue in the face about cured finishes and their safety, but that carries no more weight than a grain of sand on an endless beach. If I do not satisfy the clients needs/wants, they look elsewhere. It's just that simple.
Having said that, I use and believe in lots of petroleum based finishes, as well as others that are toxic until fully cured. For those who prefer something else, I offer those as well, so everybody's happy.
You could in fact use Shellac on a cutting board if you wanted to, but I would not choose it personally. Cured shellac can be liquified with alcohol, so unless you're mixing drinks on your cutting board and you spill some of your drinks on the board, you're probably going to be ok. Shellac is more of a film finish and as such, would not be the best choice (IMHO) for something like a cutting board that you use a knife on. Shellac does in fact dry, it can however become liquid again if exposed to alcohol, whereas most cured finishes are resistant to liquefaction once fully cured, lacquer being an exception… Shellac was used on furniture for many years and is still the preferred finish on some high end pieces. I like General Salad bowl finish and use it on some of my production bowls. It has a nice luster, that's not too glossy and it's resistant to staining. Very nice indeed!
As for the safety of Walnut oil with those who suffer nut allergies… Good question, my answer: Maybe.
I always ask my clients up front what finish they prefer and let them choose. The problem with saying it's safe for those with nut allergies is that some of these folks have very
severe allergic reactions when nuts are even in the same room with them… I saw a documentary on TV that showed a small boy who could not even smell a peanut without going into shock. His mother said they could not have a single peanut in the whole house and his friends could never eat peanuts before visiting. Just smelling them on their hands was enough to send him to the hospital.
So, who knows. I let the client decide and offer them the choice, or if I'm selling spec bowls, I tell them what finish was used. If I had a client with a nut allergy, I would not
advise them to use a nut based finish. Why take the risk (no matter how small) that some small child somewhere might be sensitive to any trace amounts of compounds in the oil? Better safe than sorry. They could always use beeswax, mineral oil, or nothing at all. Some of my clients want no finish whatsoever on their Treenware. Many years ago, this was standard practice, so that's another option for the nut allergy folks as well. YMMV. Take care and all the best to you and yours!
EWW, WVP, EWWFS
THE Woodlands, Texas