Practice question · Multiple choice
A plain silver bromide emulsion is completely blind to red light, and yet modern film records red perfectly well. How did nineteenth-century chemistry extend sensitivity first into the green and then across the whole spectrum?
Hints
- The halide itself was never made red-sensitive.
- Something else absorbs the photon and hands the energy over.
Show the answer
D. Dyes adsorbed on crystals absorb longer wavelengths and transfer energy, found by Vogel
Why
By dye sensitisation. The halide crystal still cannot absorb red light; a dye adsorbed on its surface does, and transfers the energy to the crystal. Vogel found the effect in 1873, orthochromatic emulsions followed, and panchromatic plates arrived in 1906, an addition to the crystal, not a change in it.
Practise The Latent Image
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