I am fairly new to oil painting. Please explain the differences between refined linseed, cold-pressed linseed, boiled linseed, double-boiled linseed, etc. I am confused with the variety and would like to know the drying times and how these affect the quality of the painting?
I am not a painter in any sense of the word. Using a search engine, I found this site. While not being exhaustive, it explains some of the information interesting to you.
REFINED LINSEED OIL
This is the most popular form of oil medium. It slows down the drying time of the paint, and when painting in layers, this can be very useful. Apply the ‘slow over fast rule’ – paint your fast-drying layers first, and then each layer on top should take longer to dry than the previous one. You can therefore apply more of this medium with each layer.
The [brand name] Refined Linseed Oil increases gloss and transparency as well as smoothing the consistency of oil paint.
There is also a Cold Press Linseed Oil by [brand name], which is a high quality oil often used when grinding pigments, to create oil paint at a professional level. It dries more slowly than Refined Linseed Oil, taking up for four days, and has a shinier and harder finish.
Other information can be found using search engines. If you want to actually improve your painting skills, you might want to attend some classes led by a professional.