Whitening fossils and casts to enhance photographic detail has evolved from the early twentieth century in step with advances in photography in both film and digital technologies. Whitening began with clouds of NH4OH and HCl being blown together to form a fine white coating of NH4Cl. The wet method has disadvantages in not being very stable and forms thick coatings in humid environments. Heating dry NH4Cl in a calcium chloride drying tube and variously expelling it in a concentrated vapor came into use in the mid twentieth century. It is a more advantageous method and the one commonly used by most invertebrate palaeontologists. Most dry methods differ in delivery of air to the heated drying tube (blowing over superheated NH4Cl) - directly by mouth, squeeze bulb, aquarium aerator, compressed gas bottle, or from a centralized compressed air system. It produces a fine-grained coating and works best when performed in a fume hood. Heating antimony in a drying tube or burning magnesium ribbon to produce whitening vapor or blowing fine grained powder with an airbrush have their adherents but are rarely used. Whitening electronically is a technique in its infancy but holds a great promise, especially in photography of large invertebrates and vertebrates.
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