Mineral oil is an extremely popular and common wood finish. It’s popularity is largely due to its cheap price, lack of caustic smell, and ease of use. It makes for an easy to use product that generally performs well. Mineral oil simply soaks into the woods surface and fills pores, which prevents absorption of food odors, eases cleaning, and maintains wood integrity. It also provides a pleasant luster, and unlike varnish it does not create a protective coating over the wood that is not safe for food products.
Mineral oil is a byproduct of refining crude oil into gasoline. There are varying grades of mineral oil. The lesser refined mineral oil is a grade 1 carcinogen, meaning it is definitely carcinogenic to humans. Similar to cigarette smoke, it may cause cancer and other health problems. Highly refined mineral oil is categorized as group 3 carcinogen, meaning it is not thought to be carcinogenic but the available information cannot sufficiently classify them as harmless.
Food grade flaxseed oil on the other hand is made from cold pressing flax seeds. It is edible and commonly used in Europe as a cooking oil. It is better than other natural drying oils such as walnut oil or poppy seed oil because unlike those oils, when polymerized flaxseed oil does not spoil. Flaxseed oil soaks into the wood grain's pores, leaving a shiny but not glossy finish that truly showcases the natural beauty of the wood like no other. Over time or with heat (185 degrees Fahrenheit) flaxseed oil will polymerize—becoming a strong natural finish that accepts additional layers. It is also known for bringing out a wood's warm hues.