Mountain dweller, I've used a lab in WA, but they were rather expensive. I could dig the name out for you if you like. On the question of Metal dust, the landscape supplies might have been using the term in the colloquial road construction sense, where 'metal' refers to crushed rock. Wikipedia has the following "...Applying gravel, or "metalling," has had two distinct usages in road surfacing. The term road metal refers to the broken stone or cinders used in the construction or repair of roads or railways, and is derived from the Latin metallum, which means both "mine" and "quarry" ...and I don't think cinders in this context refers to lightweight charcoal fragments.
Yesss. How can non-native speakers hope to really learn it, when it's barely comprehended by the (assumed) native-speakers. Spread something around the world and it will just naturally spawn landraces.
"Yesterday is history; tomorrow is mystery; today is a gift, that's why it's called the present." E. Roosevelt "If the world is to end tomorrow, I would plant an apple tree today" Martin Luther