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Commonly used developers are hydroquinone, monomethyl para-amino phenol sulfate, and phenidone. Other common developing componenets include accelerator, sodium carbonate or borax, sodium sulfite, and potassium bromide as an antifogging agent.


  • Developers are skin and eye irritants and in many cases strong sensitizers. Monomethyl-p-aminophenol sulfate creates skin problems and allergies to it are frequent.
  • Hydroquinone can cause is a mutagen and causes depigmentation and eye injury after five years of over exposure. Some developers also can be absorbed through the skin to cause severe poisoning. Phenidone is only slightly toxic by skin contact.
  • Most developers are moderately to highly toxic by ingestion, less than one tablespoon of monomethyl-p-aminophenol sulfate, hydroquinone, or pyrocatechol can be fatal for adults. Symptoms include ringing in the ears, nausea, dizziness, muscular twitching, increased respiration, headache, cyanosis (turning blue), methemoglobinemia, delirium, and coma. With some developers, convulsions also can occur.
  • Para-phenylene diamine and its derivatives are highly toxic by skin contact, inhalation, and ingestion. They cause severe skin allergies when absorbed through the skin.
  • Sodium hydroxide, carbonate, and other alkalis are highly corrosive by skin contact or ingestion. This is an acute problem with the pure and concentrated stock solutions.
  • Potassium bromide is moderately toxic by inhalation or ingestion and slightly toxic by skin contact. Symptoms of poisoning include somnolence, depression, lack of coordination, mental confusion, hallucinations, and skin rashes.
  • Sodium sulfite is moderately toxic by ingestion or inhalation, causing gastric upset, colic, diarrhea, circulatory problems, and central nervous system depression. If heated or allowed to stand in water or acid it decomposes to sulfur dioxide, which is highly irritating by inhalation.


  • See the section on Mixing Photochemicals for mixing precautions.
  • Do not put your bare hands in developer baths. Use tongs instead. If developer solution splashes on your skin or eyes immediately rinse with lots of water. For eye splashes, continue rinsing for 15-20 minutes and seek medical attention.
  • Do not use para-phenylene diamine or its derivatives if at all possible.

Disposal of Photochemicals Processing

  • There is concern about just dumping photographic chemicals down the drain. Old or unused chemical solution, toners, chromium and non-silver solutions are hazardous waste
  • Alkaline solutions should be neutralized before pourig down the drain. This is done with the stop bath or citric acid; use pH paper to ensure it has been neutralized to pH 7.
  • Left over stop bath can be poured down the drain once mixed with wash water.
  • Fixing baths should never be treated with acid because they contain sulfites and bisulfites which will produce sulfur dioxide gas.
  • Fixing baths contain concentrations of silver thiocyanate, above the 5 ppm of silver ion allowed by the U.S. Clean Water Act. Collect fixersto pour in the silver recovery unit.

Intensifiers and Reducers Processing

A common after-treatment of negatives and prints is intensification or reduction. Intensifiers include hydrochloric acid and potassium dichromate, or potassium chlorochromate. Reduction of negatives is usually done with Farmer’s reducer, consisting of potassium ferricyanide and hypo.


  • Potassium dichromate and potassium chlorochromate are probable human carcinogens, and can cause skin allergies and ulceration. Potassium chlorochromate can release highly toxic chlorine gas if heated or if acid is added.
  • Concentrated hydrochloric acid is corrosive; the diluted acid is a skin and eye irritant.
  • Potassium ferricyanide is slightly toxic, but will release hydrogen cyanide if heated or exposed to strong ultraviolet light. Cases of cyanide poisoning have occurred when treating Farmer’s reducer with acid.
  • Potassium permanganate and ammonium persulfate are oxidizers, causing fires or explosions when contacting organic materials.


  • Chromium intensifiers are the least toxic intensifiers but are probable human carcinogens. Gloves and goggles should be worn when using intensifiers and mixing powders must be done with a toxic dust respirator. Do not expose potassium chlorochrome to acid or heat.
  • Do not use mercury, cyanide or uranium intensifiers, or cyanide reducers because of their high or extreme toxicity.
  • Although the safest, do not expose Farmer’s reducer to acid, ultraviolet light, or heat.

Mixing Photochemicals Processing

Photochemicals can be bought in liquid or powder form, needing diluting and dissolving.


  • Developer solutions and powders are often highly alkaline and glacial acetic acid is also corrosive by skin contact, inhalation and ingestion.
  • Developer powders are highly toxic by inhalation, and moderately toxic by skin contact, due to the alkali and developers themselves [see Developing Baths].


  • Use liquid chemistry whenever possible, rather than mixing developing powders. Pregnant women, in particular, should not be exposed to powdered developer.
  • To mix powdered developers use local exhaust ventilation or wear a toxic dust respirator.
  • Wear gloves, goggles and protective apron when mixing concentrated photochemicals. Always add any acid to water, never the reverse.
  • In case of skin contact, rinse with lots of water. In case of eye contact, rinse for at least 15-20 minutes, preferably using an eyewash station, seek medical attention.
  • Store concentrated acids and other corrosive chemicals on low shelves to reduce the chance of face or eye damage in case of spills.
  • Do not store photographic solutions in glass containers.

Other Hazards Processing

Other chemicals are also used in black and white processing include: formaldehyde as a pre-hardener, a variety of oxidizing agents as hypo eliminators, sodium sulfide, silver nitrate, solvents for film and print cleaning and concentrated acids to clean trays.

Electrical outlets and equipment present hazards due to the risk of splashing water.


  • Concentrated sulfuric acid, mixed with potassium permanganate or potassium dichromate, produces highly corrosive permanganic and chromic acids.
  • Hypochlorite bleaches can release highly toxic chlorine gas when acid or heat is added.
  • Potassium persulfate and other hypo eliminators may cause fires when in contact with many solvents and other combustibles. Most are also skin and eye irritants.


  • Cleaning acids should be handled with great care. Wear gloves, goggles and acid-proof, protective apron. Always add acid to the water when diluting.
  • Do not add acid or heat to hypochlorite bleaches.
  • Keep potassium persulfate and oxidizing agents separate from acids and flammables.
  • Install GFCIs whenever electrical outlets are within six feet of water.

Stop Baths and Fixer Processing

Stop baths are a weak solutions of acetic acid. Acetic acid is commonly available as pure glacial acetic acid or 28% acetic acid. Some stops contain potassium chrome alum.

Fixing baths contain sodium thiosulfate (“hypo”) as the fixing agent and sodium sulfite and sodium bisulfite as a preservative. Fixing baths may also contain alum (potassium aluminum sulfate) and boric acid.


  • Acetic acid is highly toxic by inhalation, skin contact, and ingestion. It can cause dermatitis and ulcers and can strongly irritate the mucous membranes.
  • The final stop bath is only slightly hazardous by skin contact. Continual inhalation of acetic acid vapors may cause chronic bronchitis.
  • Potassium chrome alum is moderately toxic, causing dermatitis and allergies.
  • In powder form sodium thiosulfate and bisulfate are not significantly toxic by skin contact. By ingestion it has a purging effect on the bowels. Upon heating or long standing it can decompose into highly toxic sulfur dioxide, causing chronic lung problems. Many asthmatics are particularly sensitive to sulfur dioxide.
  • Alum (potassium aluminum sulfate) is only slightly toxic; skin allergies or irritation.
  • Boric acid is moderately toxic by ingestion or inhalation and slightly toxic by skin.


  • All darkrooms require good ventilation to control acetic acid and sulfure vapors.
  • Wear gloves and goggles if concerned about exposure, especially expectant mothers.
  • Cover all baths when not in use to prevent evaporation of toxic vapors and gases.

Toners Processing

Toning a print involves replacement of silver by another metal, for example gold, selenium, platinum, or iron. In some cases, the toning involves replacement of silver metal by brown silver sulfide.


  • Sulfides release highly toxic hydrogen sulfide gas during toning or when treated with acid.
  • Selenium is a skin and eye irritant and can cause kidney damage. Treatment of selenium salts with acid may release highly toxic hydrogen selenide and sulfur dioxide gas.
  • Gold and platinum salts can produce allergic skin reactions and asthma.


  • Carry out normal precautions for handling toxic chemicals as described in previous sections. In particular, wear gloves and goggles. See mixing section.
  • Toning solutions must be used with local exhaust ventilation.
  • With two bath sulfide toners, make sure you rinse the print well after bleaching in acid solution before dipping it in the sulfide developer. Make sure that sulfide or selenium toners are not contaminated with acids.
  • Avoid thiourea whenever possible because of its probable cancer status.