Applying a brushstroke of water-based pigment into wet plaster is different from using oils on wood or canvas—isn’t it?— although the goal is the same: make each stroke invisible. With oils, your brush can attack paint with abandon—wide blocks, long lines, quick staccatos—because with oil there’s nothing to fear: make a mistake? No problem. You can change it. Oils are pliable for ages; you can retouch, push, pull, bend. It’s why Leonardo loved oils: oils allowed him to feed his constant discontent. And even once oils dry, change becomes them. When you add a new layer, colors don’t muddy, they become more vibrant, interest bubbling beneath. In oils, a perfect brushstroke is all about blending layers. No wonder oils are so good at capturing life: like people, oil paintings are created by blending together weeks, months, years of layer after unexpected layer.

Applying pigment into fresco, on the other hand, is terrifying. You get one chance—one day—when the plaster is wet, and once it dries, you can’t change it. And you can’t mix colors in fresco, either; they’ll muck brown. During the first hours of frescoing, when the plaster’s so wet that it doesn’t want to absorb pigment, you must press hard with a dry brush, but not so hard that you destroy your smooth surface. Once your basic blocks of color are drawn in and the plaster starts to dry, build up your colors with quick, confident strokes—a hundred brushstrokes a minute; your arm will never burn like it does during this stage of frescoing. I don’t even stop for pulling up sleeves and rolling wrists during this stage; there isn’t time. Near the end of the drying process, the plaster laps up paint like parched soil, and your brushstrokes must be short and true because they harden fast as polish.

As dusk dropped that winter day and the plaster dried hard, I touched in the final bit of Plato’s white beard; if I’d needed one more stroke, I wouldn’t have made it. I lowered my brush; my arm—shoulder to fingertips—throbbed. My eyes scanned the blue sky and clouds under that central arch all the way down to Plato’s aging face and scraggly beard . . .

I don’t want to boast about how those crowds reacted whenever I finished a new giornata. Do you like talking about the reception of your work, or do you prefer when someone else does the lauding? But, for context’s sake, I should provide a couple of details to help you understand how I felt in those days. Please, forgive me. I’ll be brief. I promise.