Bromide Drag

Bromide is a by-product of the reduction of silver bromide to metallic silver by the developer. The issue is that the bromide reduces the reaction rate (it is part of the compensation mechanism) but it is usually denser than the developer and will therefore (if given sufficient time) run down the face of the negative while it sits in the tank.

The effect will cause darkened (thin, underdeveloped) streaks below very strong highlights, e.g. street lights in a night scene. The direction of the streaks depends on the orientation of the film in the development tank because the effect is caused by gravity.

More frequent agitation will mix the bromide in with the developer and prevent streaking. It shouldn't occur unless the film has been sitting in dilute developer for significant time (20 minutes?) with no agitation, the time required being dependent on the specific gravity and concentration of the developer and the strength of the highlights.

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