The stirrups are likely either rubbing on the boot causing scuff marks or they could be silver plated and the tarnish is rubbing off onto the boot. You should give the stirrups a thorough cleaning, and if they are silver polish them with a silver polish. The stirrup may also be too small in which case they will continue to rub even when clean. Remember a stirrup should be a full half inch wider than your booted foot to prevent rubs and getting caught up in it.
Silver in the fine powder form is black, that is happening on slight friction of silver metal, which is soft
hg
You are most likely referring to silver which will tarnish with time and often turns black (although depending on the composition of the gas its exposed to it can turn any colour of the rainbow)
Silver Oxide forms on the surface. The only metal that does not Oxidize is Gold.
copper,and some precious metals, when exposed to air, turn black, like silver(completely turns black when exposed to air),gold(black spots appear),and others,maybe platinum.
ya but it wont turn out well...
There is no 'uniform' for Heavy Metal, and makeup is more common to wannabe Glam Rock than it is to true Metal (corpse paint and such used by the Black Metal sorts notwithstanding). Heavy Metal is in part about individuality. Trying to turn it into a uniformed thing is completely anathema to that.
Magnesium is a metal
The metal covers are not part of the boot. The boot should have a raised lip that will allow you to work it off of the spark plug. Twist and turn it until it pops off.
You are either born black or not, and you can't simply "turn" black at will.
because if they get old they turn black
Not naturally it can't turn black.