HOME > FILM > BPFB-18
Film: BPFB-18
Presentation and Use
Blue-sensitive film of moderately high contrast. It can
be used for copying continuous-tone B&W pictures and for making high-light
masks. BPFB is especially useful, however, for making both interpositives
and, subsequently, duplicate negatives from original B&W negatives.
This two-step duplicating process allows great control over the quality
of the final negative and permits the making of either same-sized duplicates
(by contact), or enlarged negatives. Enlarged duplicate negatives are
commonly used in alternative processes (platinium, palladium, gelatine
and gum bichromate printing, print-out paper etc..), for all of these
processes require a film ‘’at’’ the finished size.
Supports
The same emulsion is coated onto both films, the difference
being the thicknesses of their respective bases (BPFB-10 : 10µ,
BPFB-18 : 18µ) Both films have an anti -halation backing.
Color Sensitivity
The emulsion, being blue sensitive, has a maximum sensitivity
of about 450 nm.
Safelight
Red safelight, as from a 15 w lamp fitted with a Wratten
1A filter and placed 1 meter from the workbench, works well for laboratory
lighting. It is a good idea from time to time to test for safelight fogging.
Exposure
The following exposure values will vary from one user to the next,
and are offered only as suggestions :
For copywork of documents, using two 1000w Xenon lamps at a distance of
1 meter , or two 45 A arc lamps : 20 seconds at f/ 64
For contact printing, the exposure time is about 7 seconds using diffused
lighting.
If the light intensity of the contact printer is adjustable, it should
be at 20 lux/second.
Development
Any good, standard continuous tone film developer, in tray, machine,
or tank, can be used to develop BPFB-18.
Fixing and Washing
After development, the use of an acid stop bath is recommended
as it will help preserve the fixer. Minimum fixing time in a fresh fixer
should be 7 minutes for a normal fixer, and 5 minutes in a rapid fixer.
Storage
BPFB-18 films must be kept in a cool and dry place, ideally at
a temperature not exceeding 21°C (68° F), and at a relative humidity
of 50%.
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