Blue Toner (Iron)

Blue Toner (Iron-based) is a dramatic blue-shift toner for B&W silver-gelatin prints — converts the metallic silver image to iron blue (Prussian blue) through a two-bath process that produces a striking cool-blue color shift. The Prussian-blue compound is the same blue used in cyanotype prints (and historical blueprints) — but applied to a silver-gelatin print rather than a sensitized iron-based emulsion.

Key features

• Two-bath process: bleach (potassium ferricyanide + potassium bromide) → toning bath (ferric ammonium citrate + sulfuric acid)
• Dramatic blue color shift — most pronounced on chlorobromide papers
• No archival benefit — iron blue is not more permanent than untoned silver; choose for color, not for permanence
• Reversible in alkaline solution — bath can be undone if the result isn't what was intended

Workflow

1. Print → develop → stop → fix → wash thoroughly (any residual fix prevents toning)
2. Bleach bath: 1-3 min in dilute potassium ferricyanide; converts silver → silver bromide
3. Brief water rinse between baths
4. Toning bath: 1-3 min in dilute ferric ammonium citrate + acid; converts silver bromide → iron blue
5. Wash: 10-15 min running water
6. Optional second pass: re-do bleach + tone for stronger blue

Practical notes

• Choose blue toner for dramatic color shift — the result is unambiguously blue, not subtle
• Best on chlorobromide papers (Forte Polywarmtone, Oriental Seagull); less dramatic on bromide papers
• The toning is shadow-first — highlights stay paper-white longer than mid-tones and shadows
• Reversible by 5% sodium bicarbonate solution if result is too strong
• PPE: nitrile gloves and eye protection; ferricyanide is mildly toxic

Related recipes

• [[recipe-krst|Kodak Rapid Selenium Toner]] — archival toner alternative; subtle warm shift
• [[recipe-gold-toner-gp-1|Gold Toner (GP-1)]] — alternative cool-blue toner with archival benefit
• [[recipe-copper-toner|Copper Toner]] — opposite warm-color shift