MITRA Forum Question Details

Hi Koo

You are probably have more experience with metalpoint than anyone else on this forum so I would defer to you on moist issues associated with the technique.

I do not see an attachment but will try to comment.

As far as fixatives, they are certainly a mixed blessing but are sometimes necessary. Too much will darken the paper or gesso ground due to surrounding the fibers/filler with a material of higher refractive index. Just the right amount will help keep the particles from being too friable. Obviously only non-yellowing fixatives should be used if possible.

I do worry that if there is enough fixative to slow or stop oxidation/sulfation that the surface would really be quite saturated, changing the overall effect. Of course, this is an aesthetic decision and the result may be just what the artist is looking for (like your preference for lightly varnishing your egg temperas).

I do not know what materials are used to finish Plike papers but they are obviously more than simply 100% alpha cellulose or they would not have the advertised feel of plastic and rubber and be resilient enough to take a metalpoint line without damage. Perhaps the surface it too compact to hold onto the abraded metal lines or one of the ingredients has a deleterious effect on the metal? This would require more testing to make a determination on this subject. I am very intrigued by your tests showing that the metal lines can actually “disappear” when they are overexposed to sulfur. I cannot imagine what the chemical process would be.  Was this liver of sulfur or another sulfur containing compound? If the problem is the paper having too slick a surface, a fixative my help, if it is chemical, it likely would not.

Sorry that is not a very definitive answer but it is all that I can say given my limited knowledge here.

I had forgotten about Tom Mazullo and Susan Schwalb. I will be purchasing that book immediately.

Plike papers may start out as 100% alpha cellulose but they must be adding other materials, sizes, etc, to make a paper that can be described as having the feel of a combination of plastic and rubber. Alpha cellulose should only be a polymerized polysaccharide.

I am now wondering if it is not acidic conditions that are causing a chemical conversion of the metallic lines. Vinegar causing lines to disappear makes far more sense as metal acetates are often more transparent than alloys. Onion and garlic both contain sulfur groups that when in contact with moisture will convert to sulfuric acid. This is why your eyes hurt and tear when slicing onions. Perhaps a similar thing is occurring with the liver of sulfur.

It would be very interesting to see if the same effect occurs in a desiccated environment. I once put a silverpoint drawing in a drying oven for a week or so and the lines definitely darkened some.  When I get some spare time, I will do the same but include some liver of sulfur. Perhaps this will accelerate the sulfation of the silver but because of the very low moisture no acidic conditions would be created.

As to varnished metalpoint drawings on panel, the famous unfinished Saint Barbara by Van Eyck is essentially a varnished metalpoint drawing on a chalk glue ground with a bit of oil paint.

​I've reached out to the Plike importer for more details on this paper and recommendations regarding fixatives. Will post if I get a reply.

​Thanks Matthew. I was planning on doing the same but your assistance is of great help.

​The Plike importer has reached out to the manufacturer for more information, but is not sure they will be willing to disclose any details of the coating formula. He said, quite directly, that Plike is not clay coated, and mentioned twice (with emphasis the second time) that Plike is made for commercial and packaging applications, and is (as we already know) not made expressly for metalpoint. (The trademark name "Plike" is apparently derived from "plastic-like".) He offered to recommend some other papers, and I said, for now, I would like to focus on Plike, for the benefit of artists using it, and conservation specialists who might have to treat works on this stock. I said that there would be interest in even the broad category of polymer used, and any recommendations for fixatives/top coatings. He did say to stay tuned, so there may be more to come.