I notice every brand's porcelain * is smooth only @ the top ( near
plug cable ), never smooth around +ve electrode, so users cannot
scrape off all the soot around +ve electrode ( to prevent short
circuit ), & must buy new plugs. www.aa1car.com/library/sprkplg2.htm
I'll put sodium § silicate ( liquid glass ) on new plugs' * before I
use them, & scrape off § ( with soot on top ) so I need not buy new
plugs as often as manufacturers want.

No wonder metal prices ( e.g. copper ) rise fast, because many
manufacturers force users to use more of their products.  If
govnmnts don't stop this, higher & higher metal prices will cause
more & more thefts ( e.g. of electric cables ) & so more power /
phone lines stolen.