Oil gilding, sometimes called mordant gilding is a technique using an oil size made of linseed oil and turpentine.
Being waterproof it is primarily used for outside gilding on metal, stone or marble or inside castles and stately homes on decorative mouldings and sculpture.
In restoration, I use this technique on XIXth century frames when there is a mixture of oil and water gilding or on objects with a lot of fine detail.
I also use oil gilding in many of my art works to transform found objects gleaned from woods or field into something other.