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The spirit photograph functioned less as evidence of ghosts than as evidence of an apparatus producing beyond intention. Double exposures, emulsion artifacts and light leaks were not failures of the photographic process, but points where the technical procedure diverged from the image sought. Rather than belief in spectral presences, it was technical divergences themselves that made the spirit photograph culturally operative. The anomalous mark on the plate became a site that demanded return, documentation and refinement of method. The apparatus had revealed a threshold – a repeatable zone of transformation where input-equals-output becomes partially unpredictable and the operator loses control – and that very threshold enforced a practice around it.
