We present results of Si-29-nuclear magnetic resonance experiments on a large number of KOH solutions in which silicon has been dissolved. The goal of the experiments is to clarify the chemical composition of concentrated alkaline solutions after etching of silicon. It is confirmed that the initial etching product of wet-chemical etching of silicon in KOH is a silicate monomer. Increasing the silicon content of the solution gives rise to silicate polymerization products. The often reported aging of etching solutions is due to silica in the etchant.