Sodium Palladium Chloride

Palladium chloride (PdCl₂ or sodium tetrachloropalladate Na₂PdCl₄; CAS 7647-10-1 / 13820-53-6) is the palladium source for palladium printing and mixed platinum/palladium printing.^[1] Palladium is the chemically-related noble metal directly above platinum in the periodic table — same sensitizer behaviour under iron-oxalate photoreduction, but meaningfully cheaper and producing warmer image tones (brown to reddish-brown rather than platinum's cool neutral). Many contemporary Pt/Pd printers run pure-palladium prints for cost reasons and reserve platinum additions for specific tonal effects.

Photographic uses

• Palladium printing: Sensitizer mix of ferric ammonium oxalate + palladium chloride, coated onto watercolour paper, exposed under UV through a negative, and developed in potassium oxalate or citrate solution.^[2] Produces warm-tone brown metallic palladium images with nearly the same tonal range and archival quality as platinum.
• Mixed Pt/Pd sensitizer: Contemporary formulas mix palladium chloride and potassium chloroplatinite in tunable ratios; workers typically settle on a preferred ratio (often 80% Pd / 20% Pt) that balances warmth, contrast, and cost.
• Palladium toning of silver prints: Dilute palladium chloride solutions tone silver prints toward a warm brown, with some permanence improvement.
• Historical surrogate for platinum: During platinum shortages (1930s–1940s wartime), palladium was the primary Pt/Pd reagent. Modern workers choose it for cost and tone preference rather than necessity.

Practical notes

Supplied as dark brown crystalline powder (the sodium salt form is sometimes supplied as a solution). More expensive than the base reagents but substantially cheaper than platinum — roughly $50–80 per gram in 2026.

Solutions in water dissolve slowly; some formulas pre-dissolve with a small amount of hydrochloric acid to accelerate. Dissolved palladium chloride produces a yellow-brown solution that keeps well in amber glass.

Related compounds

Potassium chloroplatinite is the platinum sibling — same sensitizer mechanics, different tone, higher cost. Chloroplatinic acid is the Pt(IV) form sometimes used in alternative Pt/Pd recipes. Gold chloride shares the noble-metal chemistry for a different application (toning rather than direct printing).