Can't remember where I've found this exactly , but being from 2010-2012-ish, hope they will not mind. There's probably more good in keeping it online than letting it disappear.. It's a presentation put together by Bronwen Grimes, an artist at Valve at that time. The focus is on the techniques that can be used to create diversity while keeping the "pack" low (size & memory use). Playing with shaders and decals, repetition can be avoided (limited) and there are many tricks that can lead to good looking results. Hope you find it inspirational. I think it's a nice read.