Ferric chloride dissolves copper and brass selectively — covered areas resist (resist patterns are how PCBs and intaglio plates work). Left to dwell, the surface goes through warm rust-brown into a soft, deeply textured patina. Used by jewelers, printmakers, hobbyist circuit-builders.
FeCl₃ in aqueous solution (~40% Baumé) etches copper at 25–50 °C, ~1 µm/min. Reaction: 2 FeCl₃ + Cu → CuCl₂ + 2 FeCl₂. Protected (resist-coated) regions remain at original surface; exposed regions deepen and texture. Long dwell times produce CuCl₂ + Fe(OH)₃ residues that give the warm rust-brown patina look. Standard PCB-etchant; in jewelry / metalsmithing used for relief texture and color.
character — warm copper-brown to ruddy, soft texture in etched zones, recess-shadow contrast.
Hughes & Rowe The Colouring, Bronzing and Patination of Metals (Crafts Council, 1991, Watson-Guptill ed. 1995); American Institute for Conservation patina-conservation guidelines.
House vocabulary — terms ForMatter uses with intent.
Materials and processes for people who design and make things.
A local-first library of materials, processes, applications, and finishes — equal weight, citable everywhere, so a student can move from "what is this" toward "what's actually buildable here, now, by me." Part of the renato.design ecosystem — sibling of Plenum, Specimen, Ingenue, gesture, graf, and the Renato Rhino plug-ins. Form and matter, inseparable.
Half of teaching materials is teaching how the material is made into the thing. The standard subscription library was always light on that half. The wedge here isn't better samples or a prettier interface — it's treating Process as a peer entity, not a footnote.
Conway, Lefteri, Forty, Sparke, ASM, GIA. Every voice: Voices.
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