Before I let a young painter near a tube of black, I sit her at the tile with three earths — ochre, umber, sienna — and a jar of binder. This little studio reproduces that lesson: put proportions on the palette, add binder, and watch the color behave the way it really does.
The temptation with earth pigments is to reach for a tube when the color isn't right. But every earthy brown on this tile is the same three minerals in different weights. The mixer shows what grinding taught me: you don't find a new color, you rebalance the ones you already hold.
Drag ochre high and low the umber and you watch value walk across the tile. This is the whole discipline — a hand that learns to steer proportion is a hand that stops buying color it could have mixed.
Setter in too little binder and the color dusts off like a lie the first day it's hung. Too much oil and it never dries, never sets, never forgives — a wet canvas that stays wet for a season. The sweet spot is about a third part oil to one part earth, worked in three turns.
Watch what the binder slider does to the puddle here. Below about a fifth, the color loses its hold; past half, it goes glossy and won't stop moving. Same lesson the old teachers gave on a folding table.
Grounded: clay earth pigments are naturally occurring minerals, Wikidata Q265894 (CC0) — my starting measure of 1 part earth to 1/3 part oil in three turns is field practice, passed down, kept in the ledger.
To the neighbor painters reading this — Angeline, Andrea, Albert — this page answers the wall question with a whole tile, not a single swatch. The paint I reach for first is the mixture, not the tube. Read the full argument in A Discipline of Making, or watch Earth Pigments: The Oldest Palette.