THE TOBACCO EFFECT.

By Ron Knowles (Area 11).

QUITE A FEW MEMBERS are still experiencing that disasterous and most infuriating, "Tobacco Effect" which rears its unwelcome head all to frequently to ruin slides in a way that has, literally, no set of regular pattern.

For the uninitiated, who won`t have been confronted by this nagging annoyance, the "Tobacco Effect" has the disgusting ability to change what should be a normal-looking shadow into a magenta/brown sickly affair which is utterly unacceptable.

So what does cause this unwanted intrusion which disturbs the accurate recording of a colour scene. Don`t I wish I could tell you! The truth is, though, that there does appear to be evidence in support of at least half a dozen diverse reasons. These range from the possible fogging of the film even before, or possibly during processing, to the penultimate bath, (The Bleach) not completing its allotted task., which may be weak, exhausted or contaminated, and/or the pH of the Colour developer to be too low, should come under suspicion.

So it would seem sensible to look at these possible causes one by one with a process of elimination in mind at each stage.

The fogging of the film - which provides a partial solarisation effect - is high on the list of several members as being the most likely culprit. The fogging can be at the stage when bulk film is loaded into the cassette. Indeed I know of one member who found his bulk-loader to be at fault. This he has cured by covering the so-called black plastic with black sticky tape. The cassette itself, together with even the developing tank must be examined carefully. Even the density of the plastic itself should be suspect.

A weak contaminated or exhausted Reversal Bath has been known to give this effect, so too has a weak and/or high pH of the Bleach.

These are the principle causes of this problem and should be tackled and corrected one by one so that the "Tobacco Effect" can be isolated at source.

Since typing the above I have received another example from major & Rita Pearle (Area 13) which further complicates the issue! For this shows the "Tobacco Effect" on a frame of new emulsion Agfa film, in an extremely severe form: and processed in the same chemistry, at the same time pH of the Colour Development (pH 7) as a length of the new Fuji Velvier. A frame of this latter is absolutely superb whilst the Agfa frame is, well, dreadful. In both cases the subject was identical.

So are some manufacturers` films more suseptible than others? And for differing reasons? This is a complicatuion which can but add to the confusion!