That is a good article and those are good illistrations. However the pictures only show the effects of heat range. It doesn't show the effects of various types of fouling. Such illustrations used to be common and could be found in nearly any spark p;lug catalog. They seem to be hard to find these days. The pictures you posted show classic "modifier" additive deposits. Some brands in certain areas seemed to have more such additives than others. In my area, Mobil doesn't seem to use such additives, at least not in quantities to do that. Just try some other brands and see what happens.
