Collodion Ratio Calculator
Enter a multi-part ratio from your own reference source and a target batch size to see each part scaled proportionally.
Scaled batch
Before any chemistry: safety
- Read the safety data sheet first. Get the current safety data sheet for every chemical before you open it, and follow its handling, storage and first-aid sections. The arithmetic on this page does not replace it.
- No flame or spark near ether or collodion. Collodion is carried in ether and alcohol. Ether is extremely flammable, its vapor is heavier than air and can travel along a floor to an open flame, a pilot light or a spark. Work with good ventilation, keep every ignition source out of the room, and keep containers closed.
- Gloves and eye protection for silver nitrate. Silver nitrate causes severe skin burns and serious eye damage. Wear chemical-resistant gloves and splash goggles whenever it is open, and know where the eyewash or clean running water is before you start.
- Never use a cyanide fixer. Potassium cyanide appears in period texts as a fixer. It is fatal if swallowed, inhaled or absorbed through skin, and it releases hydrogen cyanide gas on contact with acid. Never use it: modern practice fixes with sodium thiosulfate.
- Acid goes into water. When a label tells you to dilute an acid, add the acid slowly into the water, never water into the acid, so it cannot boil and spit.
- Away from children, food and pets. Store chemicals locked, labeled and out of reach of children and pets. Never use food or drink containers, and keep the work area apart from anywhere food is prepared or eaten.
- Silver waste is hazardous waste. Spent solutions carrying silver are very toxic to aquatic life. Do not pour them down a drain; collect them and dispose of them under your local hazardous-waste rules.
Learn wet-plate chemistry in person from an experienced instructor. This site gives no formulas or procedures.
Scaling, not sourcing, a historical ratio
Given a documented ratio of parts — say 3:2:1 — the total number of "shares" is the sum of the parts, six in that example. Each part's volume in a target batch is simply its share of that total: part ÷ total shares × target batch size. Scale the batch up or down and every part grows or shrinks together, keeping the same proportions the original recipe called for.
This calculator is a general ratio scaler applied to the multi-part recipes common in historical photographic literature. It performs the arithmetic only and carries no chemical, safety, or sourcing information of its own.
Frequently Asked Questions
Why are historical recipes written as ratios instead of exact amounts?
Wet-plate and other 19th-century processes were documented long before standardized modern measurement was universal in the darkroom, and practitioners routinely scaled a known-good recipe up or down for whatever batch size they needed that day. A ratio travels well across unit systems and batch sizes in a way a single fixed recipe doesn't.
Does this tool tell me what the collodion recipe should be?
No. You supply the ratio parts from your own archival source, historical text, or reference material; this calculator only scales those numbers proportionally to your target batch size. It has no built-in formulation and does not recommend specific chemicals, proportions, or sourcing.
How many parts can I scale at once?
The tool here supports up to three named parts, which covers most documented ratios, but the underlying math (scaling any list of ratio numbers so they sum to a target total) works for any number of parts.
Is wet-plate collodion chemistry something I should try without guidance?
Historical wet-plate collodion work involves flammable solvents and other hazardous materials, and should only be attempted with proper training, protective equipment, ventilation, and current safety data sheets for every material involved. This site covers the history and math of the process, not a how-to for handling the chemistry.
Educational and historical-reference tool only — plain ratio arithmetic on numbers you supply. Not a chemical formulation, sourcing guide, or a complete safety guide. Historical photographic chemistry can involve flammable and toxic materials; consult current safety data sheets and a qualified instructor before any hands-on process work.