Liquid clear.. great marketing 🙂 Get some artist refined linseed oil and some gum turpentine. Its about a 2-1 mix.. 2 parts linseed oil ( or stand oil) and 1 part turpentine. I've used straight linseed oil.. just make sure it's THINLY applied. Brush it on.. wipe it down with a paper towel that is lint free.. the blue mechanic towels work well. The idea is to provide just a bit slickness to the surface. You can also use commercial medium like Zest-it or Winsor and Newton Original Painting Medium. The Zest, Winsor and DIY mediums will dry faster than straight linseed oil.. so like a day or two 🙂 Thats fast for oils