Wetwood preservation with sugar

text by Stephan Brather

The use of household sugar (sucrose), extract from the juice of the sugar cane or sugar beet, for wet wood impregnation has been used internationally since the mid-1970s. The basic ideas behind this are the relationship of the substance to the wood substance, which is largely made up of the same molecules, clarity and strength, availability and non-toxicity, which is important for restorers and disposal, as well as almost unlimited durability.

The watering tanks for the baths should be corrosion-resistant, suitable are plastic (PE, PP, GRP) and stainless steel. The liquid is sealed off from air by tightly fitting films to the surface and container wall. A suitable room climate, which keeps the bath temperature well below, or at least not above 20 °C, must be ensured, must be ensured, and all conditions should be as sterile as possible. Soaking is done in bath concentrations of initially 10% (w/w), which are increased in 10% steps to 60%, whereby the bath must be prepared anew each time. Against microbiological activity, 0.6 - 1% sodium benzoate, 0.5% Quartasept (Schülke&Mayer, quaternary ammonium compounds, alkylamines), and 0.05% Tallofin (Ashland, emulsifiers and terpenes) against mucus formation. Regular control of the solution is done by measuring the pH, which should not drop rapidly or below 6, as this would indicate bacterial activity. The solution should also remain clear and smell fresh. Otherwise, it must be replaced and the biocide concentration increased. The impregnation process is monitored by measuring with a refractometer; the concentration dilutes slightly, which is why the concentration should be slightly over-concentrated for each preparation. To prevent regular floating, a kind of weighted shelf system is installed in the tank at the Landesamt für Archäologie Dresden/Germany.

Drying can be done under slow controlled conditions in the air, under foil covers or in covered containers with regular ventilation, or, better, in a freeze-dryer with a cooled drying chamber. After final cleaning of sugar residues with damp sponges and complete drying, a coat of mica is applied.Drying, a coating with Mowilith 50 completes the preservation.