I tend to make notes on the kit instructions. If I use a different color or my own mixture, I will write the name of the paint by the part. Not always, just sometimes. On easy, less complicated builds, I do not keep any type of journal. However, I have done one detailed, commissioned build and I kept a journal with the date, time spent and notes of what was done. I am in the process of building the battleship Bismarck, (1:350), with wooden decks and two massive PE/resin/brass detail sets. I am keeping track of all of the things listed above. It is purely to keep an accurate track of how much time I've spent on this project.