This watercolour titled Docks, Alert Bay came to me in very sad condition, covered with a mottled dark brown discoloration. This type of damage is quite typical of certain alum-sized papers and is also commonly found on the margins of Phillip’s woodblock prints. The question explored in this article is “Why?”

Before treatment

After treatment

Alum has been used as an ingredient in paper sizing for at least five hundred years in Europe, and even longer in the Orient. Very early on, papermakers discovered that adding alum to traditional gelatin sizing reduced problems with mold (alum is a biocide) and increased the finished paper’s resistance to abrasion and water.

The latter quality is especially important for the watercolour artist. Without sufficient sizing, washes cannot flow over the paper, but sink directly into the sheet, and the slightest reworking will rough up and mar a soft-sized paper’s surface. Watercolour papers are made with these special needs in mind, but it was well-known by artists that soft-sized papers not made for painting could be brushed with additional coats of alum-water to improve their working properties.

Phillips was very interested in the technical aspects of his profession and would almost certainly have been familiar with the practice of sizing papers with alum. He was also introduced to the Japanese tradition of sizing woodblock printing papers with dosa – alum and gelatin solution – by the printer Yoshijiro Urushibara and he describes the method in detail in his book, The Technique of the Color Woodblock, published in 1926.

Docks was probably painted in 1927, when Phillips visited his sister in Alert Bay, with alum sizing fresh in his mind. It seems likely that Phillips alum-sized the paper to prevent rippling or uneven paint distribution, but why did the sizing undergo such extreme discoloration? One possibility is that these darker than normal discolorations are caused by the particular type of alum used.

True alum, aluminium potassium sulfate, was largely replaced by the much cheaper (and highly acidic) aluminum sulphate or papermakers alum over the course of the 19th century. True alum can be highly refined and purified, removing contaminants such as iron. Papermakers alum cannot be purified to the same extent, and is often contaminated with iron and sulfuric acid, both highly detrimental to the health of paper.

My guess is that artists like Phillips and some Japanese woodblock printers were working at the end of that change-over, and substituted papermakers alum for true alum, not realizing the difference it would make.

Fortunately, it was possible in this case to safely remove most of the discolouration with chelating agents and a mild bleaching solution and with thorough rinsing by float washing and locally applied water mist on a suction table.