Spark Plug Issue

Changed my plugs for the first time yesterday and found one plug different than the rest. It was the cylinder (1 or 4, can’t remember which) on my passenger side (LHD). The outer-metal portion of the plug had what appeared to be dried-up water deposits(calcium-like deposits) on it and the top of the plug was very black. The electrode also had a bit more carbon build-up as well.

Any ideas on this?

can you post a pic??

is it white deposits?.. the cylinder may be running weak?

I showed the plug to an experienced mechanic. He said the lead wasn’t getting good contact on the plug and it was arcing.

So, I ordered a set of Magnecors and installed them. First track days are next weekend so hopefully I’ll see an improvement.