Eastlake

​This is a question that could essentially be an entire PhD topic so I will do my best to answer. Eastlake as well as related texts (M.P. Merrifield comes to mind) from the 19th and early 20th century are certainly important documents. Not all of the technical information should be completely discounted;however, as you have already pointed out, we have now found other statements in these texts regarding materials and techniques to be inaccurate as scientific advancements have allowed to us to learn more about Flemish painting techniques. I highly recommend checking out the fairly new publication (2017) from the 2012 van Eyck Symposium entitled “Van Eyck Studies” as there are several articles within the book that provide very up-to-date information regarding van Eyck’s painting techniques. There is also the articles that can be found in the National Gallery Technical Bulletin (NGTB) series HOWEVER please note that the NGTB dates as far back as 1979 and much of what is postulated early on about Flemish painting technique has since been re-visited. We now know more about pigment degradation for instance….one example would be that “copper resinate” (dissolving copper salts in a heated solution containing resin) was probably NOT used by painters (at least not frequently) until the 17th century. We are still learning more about copper green pigments. And then there is evidence that some of these painters were adding glass particles to their paints most likely to facilitate drying (additives in glass like lead for example would leach into the surrounding oil medium). Finally it seems that vitriol (zinc sulphate) may have also been used on occasion as a drier (this material was found in van Eyck’s Arnolfini portrait…in addition to glass btw). 
But as far as pigments go, that is really it as far as “new” information if you are talking about van Eyck and even Flemish painters in general. The NGTB articles are still a good go-to for that (and they are all free to download on the National Gallery London’s website). I would also check out “Investigating van Eyck” and “Rogier van der Weyden in Context.”
The subject of binding medium however is a really tricky one. You will find people stating that van Eyckian painters occasionally coated certain pigments (like azurite) in protein in order to prevent them from reacting with the surrounding oil medium. You will find people stating that these painters occasionally applied lower paint layers using egg tempera, followed by oil glazes. You will find people stating that van Eyck used partially heat-bodied walnut oil in this and that color, etc. Well….all of these things have either been a) found to be incorrect or b) require careful and thoughtful re-visitation. Basically if you are trying to emulate van Eyckian works use oil. We really do not have the ability to know what type of oil or even how it was pre-treated contrary to what a small group of folks may claim. Is it possible that these artists may have also occasionally used resins as additives? Yes…of course. But again if they added small amounts of these things it is likely impossible for our current instrumentation to detect these now very degraded markers…particularly after these works have been restored 5, 6, sometimes 15 times. 

But we do have a sense of layering…I would advise checking out our Memling reconstruction which you can find on the Kress Technical Art History website…Lower layers were generally more opaque and even a bit on the “lighter” side, with subsequent glazes applied very thinly to further refine areas of modeling.

I hope this is somewhat helpful!

​Ben you are absolutely right! And I am sorry for not including this above, particularly as a Noelle is wonderful and was one of my outside readers for my dissertation and b) the book is a great resource (she also has an article in Van Eyck Studies btw). I think I tend to view her text as more of a “historiography” of how the conservation and scientific communities have viewed van Eyckian paintings….but there are certainly tidbits in there about technique.