Potassium Chloroplatinite

Potassium chloroplatinite (potassium tetrachloroplatinate(II), K₂PtCl₄; CAS 10025-99-7) is the platinum salt used in platinum/palladium printing — the premier fine-art alternative photographic process. Combined with ferric ammonium oxalate as the iron sensitizer, it produces contact prints of pure metallic platinum on watercolour paper, with an extraordinarily long tonal range and permanence exceeding any silver gelatin print.^[1] Platinum prints are the reference standard for archival black-and-white image longevity.

Photographic uses

• Platinum printing: The canonical use. A sensitizer mix of ferric ammonium oxalate + potassium chloroplatinite is brushed or coated onto heavyweight paper, exposed under UV through a digital or traditional negative, and developed in a potassium oxalate or citrate solution.^[2] The developed image is pure metallic platinum.
• Platinum toning of silver prints: Dilute solutions of potassium chloroplatinite tone silver gelatin prints toward a neutral-to-cool platinum colour; the toned print combines silver image density with platinum permanence.
• Mixed Pt/Pd formulations: Most contemporary Pt/Pd printing uses a sensitizer that combines potassium chloroplatinite with palladium chloride in tunable ratios; pure platinum gives cool neutral tones, pure palladium gives warmer browns.

Practical notes

Supplied as dark ruby-red or maroon crystalline solid. Very expensive — in 2026 the typical supplier price is around $100–150 per gram. Sensitizer formulas use 0.5–5 g per print, so a 10-gram container supports many months of serious work.

Solutions are relatively stable in amber glass but decompose slowly over a year or more; buy in small quantities as a cost-control measure. Dissolves readily in warm water; use distilled water exclusively to prevent process-failure from mineral contamination.

Critical: do not confuse potassium chloroplatinite (Pt(II), K₂PtCl₄) with potassium chloroplatinate (Pt(IV), K₂PtCl₆). The former is what Pt/Pd formulas specify; the latter is a different compound with different photographic behaviour. Verify the oxidation state and formula before weighing.

Related compounds

Chloroplatinic acid (H₂PtCl₆) is the hydrogen-salt Pt(IV) form sometimes used in alternative Pt/Pd recipes. Palladium chloride is the lower-cost palladium sibling, often paired with potassium chloroplatinite. Gold chloride is the gold-toning analog.