Technical strange substance on lead end of sparkplug

[Donal]

head gasket went. head is now off. will get it skimmed tomorrow. upon examining it i noticed that one of the plugs has got a brown red powder on it. doesnt look like rust. the sparking end of the plug and the inside of this cylinder has got a lot of carbon. Basically one end of plug looks rusty and the other end is sooty! btw this is not the cylinder where the gasket leaked.
Any ideas what this could be?