Uncoated lens bloom

[JPD]

Too perfect, if you ask me. Given that the finder and taking lenses have different makers and will not share the glass formula it is surprising that they should develop the same bloom. Chances are that that is a after-market coating upgrade. These were quite popular and accessible in the 1950s.

Natural bloom has a rainbow shine, like oil in a puddle of water. The after-market coatings would be blue and uniform.

 

[tunalegs]

Some lenses won't bloom because not all glass types are capable of blooming.



I have noticed however, on a couple occasions when cleaning really filthy box cameras that after cleaning the lens with windex, if do not go back and remove all traces of windex with lighter fluid or alcohol, the lens will sometimes be covered with a rainbow like sheen after drying. I assume this sheen is thin layer of soap, which coincidentally was one of the ways people could soft coat their lenses at home before hard coatings became available.

 

[Freakscene]

Maybe there is someone on this forum who knows what causes this blooming. Some lenses have it and others - the same type and the same age - do not.

Bloom formation depends on the presence of hydrogen-terminated silicon with a specific type of porous surface. The porosity occurs in specific glass types and is largely determined by cooling methods during manufacture. The hydrogen terminated bonds in the silicon are dependant on the glass chemistry and manufacturing method. The terminal hydrogen is the site where the oxidation occurs and this is why it happens in some lenses and not others.

Marty