WHAT HAPPENS DURING FILM PROCESSING

the film has been exposed and the photographer seems satisfied with his work actually he's just started the job the image thrown by the camera lens has left a record of itself on the film but the record is invisible and cannot be used until it is made permanent and visible what's more the film is still sensitive to light and will be ruined if stray light reaches it its sensitivity to light must be cancelled out ears work for the laboratory there is a combination of chemicals that will do this job of developing and preserving the photographic negative we will make up a developing solution step by step we will give each separate chemical a job to do and so turn the latent image on the film into a visible image when light strikes the silver salt particles they wake up the awakened particles form the latent image first step then is to use a chemical to blacken the latent image this chap represents that chemical which is generally termed the reducer of the many reducers available these are the most often used they do what we require so after making a solution of a reducer in water we will try to develop the negative something's not working and here's why our reducing agents act only in an alkaline solution so far our solution is not alkaline the development we're making need something to make it alkaline and speed up its action we need an accelerator sodium carbonate is the most commonly used accelerator so let's add it to our solution first the reducer now the accelerator and here goes the film there it is the accelerator is making the reducer do its work but the action is too energetic the reducer is working on the unexposed silver particles we need a traffic cop to restrain action to the latent image and give some protection to the unexposed silver salt particles the restrainer for developing solutions is potassium bromide it prevents the reducer from blackening the whole film and lets it develop the latent image correctly let's add the restrainer to our solution first the reducer second the accelerator now the restrainer now we will try another test negative that's more like it what has happened to our solution oxygen in the water attacks these chemicals quickly and soon burns them into useless condition we need protection something to preserve the chemicals that make up our developing solution sodium sulfite is the most widely used chemical for preserving photographic solutions let's make up the developing solution using a preservative now watch that negative this is the kind of developer we want the latent image has been developed satisfactorily and the solution is still good and ready for further use to stop the action of the developer at the desired point we transfer the film to the shortstop bath the effect of the acid shortstop is immediate and all developing action stops acetic acid is the active ingredient of the shortstop bath at this point our film is still sensitive to light and contains exposed and developed silver salt particles some exposed and undeveloped particles unexposed and undeveloped particles to remove the undeveloped silver salt particles we transfer the film to the fixing bath the fixing agent is sodium thiosulfate it eats away all of the undeveloped still sensitive silver salt particles when each unit of the fixing agent becomes loaded with silver salt it becomes dormant and must be displaced by fresh fixing agent the negative is now in sensitive to light but is saturated with active fixing agent if this is not washed out it will stain the negative and cause the image to fade water alone is needed to do this job extended Washington causes clumping of the silver particles and the resulting coarse-grain negative will lack fine detail after the washing has been completed wipe away all surface moisture from both sides of the film and hang it to dry in circulating cool dry air a slow drying rate will result in increased clumping of the silver particles therefore dry the film as fast as possible without the application of heat in photographic processing each step must be right know what to expect from each chemical in the various solutions there is both a minimum and a maximum time for each step the best result is obtained when the correct procedure is carried out