Copper Toner

Copper Toner produces a warm red-brown to copper-orange color shift on B&W silver-gelatin prints through a two-bath process: bleach (potassium ferricyanide + potassium bromide) followed by toning (copper sulfate + ferric ammonium citrate + sodium bisulfate). The copper-toned print sits between sepia (warm brown) and selenium (subtle warm) in tonal character — distinctively warmer than KRST but less dramatic than full sepia.

Key features

• Two-bath process similar to blue toner but with copper sulfate replacing iron salts
• Warm red-brown to orange color shift — depth depends on toning time
• Modest archival benefit — copper toning provides some permanence enhancement (less than selenium)
• Best on chlorobromide papers for the strongest warm shift

Workflow

1. Print → develop → stop → fix → wash thoroughly
2. Bleach bath: 1-3 min in dilute potassium ferricyanide; converts silver → silver bromide
3. Water rinse
4. Toning bath: 2-5 min in copper sulfate + ferric ammonium citrate solution; converts to copper compound
5. Wash: 10-15 min running water

Practical notes

• Choose copper toner for the specific red-brown aesthetic — neither sepia nor selenium produce the same color
• Tone strength depends on bleach completeness before toning bath — partial bleach gives mixed silver+copper image (split-toning)
• More popular among alt-process printers than mainstream silver-gelatin printers
• Concentrate keeps 1+ year sealed; working baths are session-use
• PPE: nitrile gloves and eye protection; ferricyanide and copper sulfate both mildly toxic

Related recipes

• [[recipe-sepia-toner|Sepia Toner]] — dramatic warm-brown alternative
• [[recipe-thiourea-sepia-toner|Thiourea Sepia Toner]] — variable warm-tone with control
• [[recipe-krst|Kodak Rapid Selenium Toner]] — subtle archival toner; less warm
• [[recipe-blue-toner-iron|Blue Toner (Iron)]] — opposite cool-blue shift using ferricyanide