I usually complete a painting in one day so I don't  worry about drying time too much.   If you need to extend the drying time, Sun thickened Linseed oil will work like Andrew Taylor says.  If you want to shorten the drying time.. I use Winsor Newton Liquin mixed with my oils (as a medium).  I also use Liquin when I re-paint a painting.  It brings the color back to life and the fresh paint you put on will match the old paint to a closer degree.  

I don't glaze rocks (or anything for that matter)... If you hit the value just right -- that will give it the luminosity it needs.  Shadows in rocks are lighter and have much more color variation in them than you might think.

Underpainting with a warm reddish grayed color works best for me in a landscape.  VERY thin transparent paint.  Look at the "How To" articles, the progression of a painting.

 Don Finkeldei

Hi Michael

There are several methods. A traditional one is 'Sun-thickned linseed  oil with maybe a small addition of Dammar varnish' I seem to remember. Sun-thickned oil is great. One has to be careful the paint  doesn't become too oily shiny.

Another drier we use is a product call  'Liquin', an alcoyd I think. I mix a lillte into each reservoir.

Otherwise I use a "Cobalt drier" I bought in Spain, (never seen it on sale in the UK) A  very small amount added to my turpentine thinners and same in the linseed oil reservoir.

 Another thick paste is "LUCAS MEDIUM  No5".  It is clear colour and makes the paint go futher and speeds drying well, but  it is thick, a similar texture to the pain. You can mx it 1:1

Hope that is  a help. If you need instructions on sun thickened oil let me know.

Regards

Andrew Taylor

Hi

 I have bought the Tim Deibler dvd and like it but I really love the way DOn and Scott CHristensen work - the colours are magical and I llike the more realistic approach as opposed to Tim Deibler.  I would like to ask many questions about drying time, underpainting involved and glazing for rocks (is this really necessary to get that luminocity) - do I need to use alkud galzing gel or any other meduim.  I have lots of Qs - would it be okay to post these ?

Ta

Michael Murphy - a great admirer of your work