I kept watching the artist dripping some liquid onto prints. During all of 12 minutes, hoping to see the resulting effect. And at the end the interpreter tells the onlookers to come back in 30 minutes, time for the acid and scarce sunlight to take effect.
Still waiting.
Yeah, that's how I understood it. That is to say, apparently there's first a layer of "brass powder suspended in a medium" (https://goliga.com/daisuke-yokota-untitled) and then a B&W photo silkscreen printed on top. The acetic acid reacts with the brass powder, altering its hue and possibly the sheen of the individual particles. I don't think the acid affects the printing ink used for the B&W layer (much).