Original Liquin is excellent for plein air artists. It extends and speeds drying of oil paints. The medium is also slippery so you can paint faster. My process is to rapidly sketch with homemade willow charcoal on linen canvas that has a clear primer. I then seal the charcoal with alkyd medium thinned with odorless thinner. The next step is to sketch the lights with thin washes of white. All of these steps are facilitated by Liquin.

This is very easy to mix into paints. It is helpful in thinning paint to do a layout on canvas, as well as creating the first lean layers while speeding up the dry time. It's smell is very strong, but does lesson significantly after a few minutes.

Winsor and Newton Liquin Original is my go to choice for oil painting medium. It’s easy to use to thin the oils and it helps them to dry quicker. I’ve used it for years. Like everything else, it has increased in price but after shopping for the best price on the larger (250 ml) bottle, Walmart beat all the rest.