Methyl Cellulose

​FYI – This entry in Wikipedia: Methylcellulose (MC)
… available in various types, grades and molecular weights, which influence their properties such as viscosity and flexibility…. Methylcellulose is known for forming stable and resilient films and being resistant to biodeterioration (Down, 2015). The bonds are weaker than these of starch paste and gelatin, but they retain strength better upon aging (Down, 2015). According to the respondents’ comments, MC is a mild (“ weak” ) adhesive that is highly hydrophilic (holding water) and dries slowly (Nasatto & al., 2015). For this reason, it used to be mixed with other adhesives, such as wheat starch paste or PVAs, to produce stronger and faster drying bonds (Feller & Wilt, 1990; Down, 2015). It also presents no discoloration and no viscosity loss upon aging (Feller & Wilt, 1990). No research was found confirming that films of MC become acidic over time, as one respondent had suggested[5]. As long as it is prepared from powder, MC does not alter the pH of the substrate. Nevertheless, Feller &Wilt (1990) point out that aqueous solutions obtained from the manufacturer might present a wide range of pH (3– 8), depending on the purity of the solution. In the experiment of Baker (1984), MC applied on paper did not affect the pH of the substrate; however, it is susceptible to either acidic or alkaline hydrolysis. Therefore, the acidity of the substrates may contribute to the degradation of methylcellulose (Feller & Wilt, 1990).

I have not used methyl cellulose as a binder for a ground. Koo, thanks for the lengthy Wikipedia info. I also do not know if it would be a good replacement for animal glue. I hope that someone with knowledge or experience with this will weigh in.
I realize that that many believe that historical grounds were either bound in animal glue or linseed oil with a transitional period where both were used. However, a survey of historical recipe books etc. will reveal that there were a really large number of ground formulations. I have seen many the use starch or flour and then a later coating of oil paint or a suffusion of drying oil. Egg-based grounds were used in the 19th century and casein was very popular in the mid-20th century, etc. Of course, none of this suggests that these were necessarily as good as the animal glue or oil, just that materials choices were not as cut and dried as we often believe.

​Yes, I’ve also wondered about casein as a binder in an egg tempera ground.  I believe the key would be the strength of methyl cellulose and casein – my understanding is that a ground needs a lot of gel strength to hold up well over time.  So, if anyone wants to comment on the strength of casein, that info would be welcome too.  (FYI, I tried the casein ground from Sinopia Pigments with egg tempera, but that ground also has a percentage of oil in it and I found the paint did not behave well on top, lifted too readily).   

​Casein is an extremely strong binder. I do wonder if some of the sympathetic qualities that we see when using egg tempera on a glue-bound ground is the slight swelling of the glue due to the application of water borne tempera. Perhaps this helps lock the paint onto the surface in a way that is not possible with acrylic and PVA bound grounds even if there is a similar absorbance. Casein is initially water soluble but become less so over time. Anyway, I have not tried egg tempera on a casein ground. I never saw the need to deviate from an animal glue-bound ground for that medium. I have played around with casein and casein emulsions when experimenting with formulations used by Arthur Dove but that is not really germane here.

I agree with you, Brian – I’m convinced that part of the compatiblity between egg tempera and an animal glue ground is that the glue remains receptive to the water in the paint (versus a synthetic-polymer binder which, once cured, repels the water in the paint).  Managing egg tempera paint is, to a large degree, about controlling the water content in the paint, and the absorbency given by both traditional gesso’s high PVC and water loving glue binder are key to doing that.