As part of a research project dealing with the modification of resonant spruce wood used by violin makers and restorers of musical instruments, the influence of water, hydrochloric acid, and solvent on the gelation time of a solution of ethyl silicate 40 was studied. (Ethyl silicate 40 is a partly condensed tetraethoxy silicate with 40% silicon dioxide, produced by Chemiewerke Nunchritz, German Democratic Republic.) The yield of silicon dioxide (SiO₂ . nH₂O) in wood after immersion in the treatment solution under reduced pressure or flotation in the treatment solution at atmospheric pressure was measured. The dimensional changes of wood during impregnation and after evaporation of solvent and water were examined.