Original: Often an oil such as linseed was boiled with a resin such as pine resin or even frankincense; these were called 'varnishes' and were prized for their body and gloss. Other oils occasionally used include poppyseed oil, walnut oil, and safflower oil.
Simplified: These include pine resin, frankincense, poppy seed oil, walnut oil, and in more modern times safflower oil.