The photographic enlargement is a step in the process of restitution of an image present on a negative film. The purpose of this step is to transfer the image (from a developed film) onto paper and to enlarge it. The contact print is another form of print that does not allow enlargement.
The raw material: the negative (the negative film, after development).
The enlarger: it is the device that exposes the film on a photosensitive paper. It is equipped with an enlarging lens whose focal length is close to the normal focal length for the type of negative used (example: 50 mm for 135 film, 75 or 80 mm for 6×6).
Paper: there are several kinds of paper depending on the characteristics of the negative and the taste (Fiber-based (FB), Resin-coated (RC), multigrade, cold, normal, hot, etc.).
Inactinic lamp: this is a special lamp (yellow-green or red) that diffuses a light whose color (wavelength range) has no effect on the photosensitive surface of the papers used for black and white prints. Without it, the operator would be obliged to carry out almost all the operations of development in absolute black.
Masks: Mounts of cardboard, cotton and wire (for example) used to mask certain areas in order to overexpose or underexpose them. Masking can also be done with the hands.
Other more or less important accessories: feeder, focusing magnifying glass, application counter, blowing brush, etc.
For an exposure to be successful, several factors must be considered (among others):
The aperture of the lens diaphragm: The lens of the enlarger can be adjusted just like the lens of a camera. The depth of field induced by the diaphragm exists well at the level of the plate of the enlarger, but it is less influential given the parallelism of the film and paper planes, however in case of straightening of lines (when it is necessary to tilt the tray that receives the paper and therefore when the film and paper are no longer parallel), this depth of field can become decisive.
Exposure time: A good habit is to set a time of about 16 seconds and to adjust the diaphragm accordingly. You can use a magnification cell to determine a basic time that you will vary according to the desired result.
The grade: There are several grades in black and white photography. Grades – determined by filters for so-called “variable contrast” papers – are used to intensify or decrease the contrast of the film. A grade 2 corresponds to a normal contrast, a grade 3 corresponds to an accentuated contrast, a grade 1 to a “soft” contrast. The grades generally range from 0 to 5 (depending on the paper marks and also on the filters used) the median grade is generally 2 (called “normal”). It is advisable to start with a grade 2 and, if necessary, to readjust.
Revealing the image (development): The developer is a liquid solution that reveals the image of the photosensitive paper. For good, reproducible results, the duration of this operation should be fixed (usually 60 to 90 seconds for so-called “variable contrast” papers). Depending on the desired overall rendering, the exposure will be varied by playing on the exposure time and on the diaphragm of the enlarger lens as well as on the grade of paper, but in no case the development time.
The stop bath: When the developer is removed, the image passes through an acid stop bath (water + acetic acid or vinegar). It is simply a matter of stopping the development reaction and saving the fixing bath. The stop bath is short and usually lasts a few tens of seconds.
Image fixing: This step allows to eliminate the still sensitive (undeveloped) silver grains that would still be present on the paper. Fixing in a “fast” fixer (ammonium hyposulphite) lasts between 30 and 60 seconds2. The use of a rapid fixative has the advantage, especially when using baryta paper, of reducing the impregnation of the fixative in the paper substrate. Residues of fixative would lead to a poorer conservation in time (yellowing of the photo). Some printers, however, prefer the use of traditional sodium hyposulphite fixers, which require a longer fixing time (between 3 and 5 min) but which would bring a better conservation in time.
Final washing: Washing is important and must be done carefully (especially if fiber-based paper is used). It can be done in a basin (washing by emptying) or in a vertical tank (continuous washing). The so-called variable contrast papers (or resinated, plasticized or RC for Resin Coated in English) are washed in 2 minutes in running water at more than 12 °C and in 4 minutes in running water at less than 12 °C2. Fiber-based papers require a longer washing time. More than one hour for a wash without auxiliaries. The use of an auxiliary reduces the washing time by 2. Insufficient washing will cause slow and progressive degradation of the photo.
Drying and Spin Drying: Before drying, prints must be spun dry. The simplest method is to spread the print on a glass or Plexiglas plate and pass a squeegee, squeegee roller, glove or other on both sides. Depending on the paper used, the drying techniques differ. The fastest method is to use an electric dryer, but this type of equipment is quite expensive. Resine-coated papers can be placed on a vertical stand and dried at room temperature or laid flat on drying racks or suspended from a wire. Fiber-based paper, electric dryer or drying racks.