The rate of thermal formation of colloids in additively colored KCl has been studied in an attempt to understand the mechanism of precipitation of the excess potassium. It is found that the process is best described as a dislocation induced precipitation, the end product being an equilibrium between the remainingFcenters and the precipitated potassium. Analysis of the rate data leads to a diffusion constant of the diffusing entity of the order of 10−9cm2sec−1to 10−13cm2sec−1. The model postulated for the formation of the colloids is the diffusing ofFcenters to a nucleation site where they combine with lattice potassium ions to form atomic potassium.