walnut oil compared with linseed oil

Richard,
As far as walnut vs linseed. I can only reiterate the general consensus on the subject . Most writers and researchers suggest that linseed oil dries the fastest and creates the strongest most resilient film when mixed in the proper amount with pigments. Walnut oil is considered next with poppy and safflower below that. This is what we have in our “Resources” section. The degree, however, to which any “inferiority” to linseed oil effects walnut oil’s suitability for oil painting is far less certain. Some have written that the slightly slower drying time may help to prevent wrinkling in paint films while others suggest that some of the film defects seen in 16th century Italian paintings are a result of their use of walnut oil. My guess is that its use is neither the panacea, nor the harbinger of doom that opinions on either extreme suggest.  To be truthful, I preferred using walnut oil in my lead white and fast drying blue paints like cobalt blue. The thinness of the walnut oil afforded the ability to make a very dense white and the good drying of the lead white would counteract and effects of the slightly slower drying oil. Yes, walnut oil may yellow just as much in the long term, but it was nice to stave off any yellowing for as long as possible.
 As to the alkyds, I think that some of this was touched on in the previous response about alkyds. It appears that the choice of oil in a long-oil alkyd medium has less of an influence on the longevity than the amount of driers and other additives. It is difficult to get the precise formulations from manufacturers, but as R. Gamblin wrote, you can get a sense of the relative amount of driers by comparing the color of the medium. Most companies use a cobalt or mixture of metal driers that contain cobalt. The cobalt imparts a violet or pink hue to the medium. Hopefully this is of some help.