Takeaway coffee cup used to hold "paint water."
I accumulated some takeaway coffee cups during the Covid lockdowns in Melbourne in 2020, as cafes weren't allowing the use of reusable cups for fear of contamination.

Layers of paint have accumulated from the reiterative action of wiping my brush on the edge of the cup to discharge excess paintwater (acrylic) and from the build up of pigment as the paintwater evaporated. The most visible pigments include ultramarine blue (PB29), phthalo green (PG7), chromium green oxide (PG17) and carbon black (PBk7). Since deciding to omit the use of acrylic paint and toxic pigments in 2022 I have stopped using phthalo green, which is thought to contain copper.