John, from what I understand, and it is backed up in the link you provided, that there is an actual chemical reaction happening between the light and tar (bitumen of Judea). It was used because this property was already observed in the tars use as a resist for engraving.
Vaughn
Vaughn
I don't see it. Can you point us to it, please?
Second paragraph (end).
"He discovered that not only was the bitumen bleached to a light gray color by its exposure to sunlight, but also it had the property of hardening against its support material due to the action of its solvents, oil of lavender and turpentine."
Poorly written, but the is the gist of it. The oil of lavender and turpentine dissolves away the unexposed (thus unhardened) tar.
Vaughn
I'd suggest that you're not seeing your keyboard, you're seeing the image of it projected on your retina.
Ahhhh, that is something I discovered that changed my photography forever. And that discovery is the simple fact that it is the action of light that allows us to see. We do not see objects -- chairs, keyboards, etc. We see light and light only. We only "see" the keyboard because of the way light reflects off of the keyboard.
In this case, I think definitions came up because some people's answers to the original question assumed "the photograph is the negative", some people's answers assumed "the photograph is the print", somebody said "what about slides", at least one person proposed that the photograph exists in some platonic form even before the shutter fires, and it was kind of clear that we weren't all talking about the same thing.
Sorry, but this still reads to me like a simple drying process of the bitumen. The dry and hardened bitumen stays and the wet and still soft bitumen is washed out by the oil. Where is the photochemical reaction?
Tar does not "dry" -- there is little or no water in it. It changes its chemical properties/make-up when exposed to UV light...that is the definition of hardening in this case. If there were no chemical change in the tar, all of the tar would be dissolved away.
But even if it was a function of removing water from within the tar by the light, that would still a chemical action -- a chemical (water) is removed selectively from a material and then that material reacts to other chemicals based on the presence or non-presence of water.
But it is important to remember that water is a chemical and that "drying", in this case, is the process of changing the physical state of that chemical (from a liquid to a gas) -- a drying towel, dried selectively by exposing it thru a negative for example, could be a photograph if one could make that change permanent
If one wants to get fussy, light does not cause the full reaction with the silver on film or paper -- it only starts it. It is the developer that takes the slightly changed silver and excellerates the change from one type of silver to another.
That sounds more like physics and less like chemistry.
A photograph is created when a print is produced that agrees with the artist's original conception.
That's my opinion. I don't think a conception that exists purely in the mind, or a negative, are photographs.
niepce's process is photographic by your definition ...
it was made using a light sensitive material, and washed in oil of
lavender ( a chemical ) is permanent + on display today at the university of texas ... the image i linked to, is the FIRST photograph.
The subject matter of physics includes mechanics, heat, light and other radiation, sound, electricity, magnetism, and the structure of atoms. This is very different from chemistry and biology. This is too basic to be discussed.
In the words of Ernst Rutherford, "physics is everything. The rest is stamp collecting".
I don't think photographs are created. I think they evolve.
Somewhat more seriously, it seems to me that photographs aren't entities that just spring into being (one moment there is nothing, and then the next moment there is a photograph).
Matt
the difference is only the subject. Prints are photographs of negatives.
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