Soluble nylon, which is prepared by reacting Nylon 66 with formaldehyde and excess methanol in a formic acid solution, has a number of properties which led to its widespread use in conservation. However, it quickly becomes insoluble upon aging. Infrared spectrometric methods were used to study the kinetics of its insolubilization and embrittlement. In the absence of water, the primary insolubilization reaction is cross-linking; in aqueous solutions, insolubilization is the result of hydrolysis and cross-linking. (Abstractor's note: This mathematical approach to the subject includes many equations and special plottings of data). See also AATA 21-1334 for entire proceedings.