Wow... When you say the colours faded do you mean the plate reverted to being completely black again (i.e. its over exposed state)?
Harry On Sun., Nov. 27, 2022, 2:58 p.m. MSF, <[email protected]> wrote: > > This effect was studied extensively thoughout the 19th and early 20th > centuries, but in another field. Early researchers in photography noted the > same effect and more in their experiments with Daguerrotype plates. A > purposely over-exposed plate would turn very dark. If the plate was covered > with pieces of colored glass and re-exposed to bright sunlight, the plate > would reproduce the colors through which the light was filtered. This no > doubt tantalized photographers with the idea of color photography, but the > effect would eventually fade and the exposure times and light intensity > requirements made that impractical. Further, there was no way to fix the > image. The same effect can be demonstrated with so-called printing-out > papers, silver chloride emulsions meant to be contact printed from > negatives without the need for chemical development. > > So, basically, this is a demonstration of one field of endeavor not paying > attention to developments (pun intended) in another. Besides, it's not nice > to second guess Goethe. > > MSF > > > > ------- Original Message ------- > On Saturday, November 26th, 2022 at 6:41 PM, H LV <[email protected]> > wrote: > > This is a google english translation of a german article that was > published in December in 2021. > > The Ultraviolet Enlightenment > > https://docs.google.com/document/d/178aIZp1ts5J1HCvWuZCkdoDvwbzp8tm_xiPGdonvPM8/edit?usp=sharing > > (The original article is here > > https://www.faz.net/aktuell/wissen/physik-mehr/entdeckung-des-uv-die-ultraviolette-erleuchtung-17687221.html > ) > > It is about Goethe and Ritter in the early 1800s when Goethe encouraged > Ritter to look for invisible radiation beyond the violet > end of the spectrum given that Herschel had just discovered evidence of > radiation below the red end of the spectrum using a thermometer. > Ritter was eventually credited with the discovery of UV light using a > light sensitive paper. > > However,as the article explains he did another experiment which was > inspired by Goethe's concept of polarity but to this > day the results have been dismissed as an error. Goethe predicted that if > UV light darkened the photo chemical paper, then infrared light should > lighten the same paper. Ritter reported finding this to be the case but > because the chemical process is irreversible subsequent scientists > have insisted that the _observation_ of lightning must have been an error. > Until 2021 no one had even attempted to replicate this simple experiment, > but now there is evidence that Ritter was probably correct in his > observation. However, a mystery remains as to why the paper should be > lightened. > (one chemist speculates the silver atoms are being rearranged so their > reflectivity changes). > > I am posting this as another example of how some observations can be > prematurely rejected on the basis of opinion instead of a proper follow up > investigation. In this case the observation is more than 200 years old! > > Harry > > >
