Artistic Chemistry: Photography

Daguerreotype of Unknown Woman c. 1850

Photos. We all have them. With the advent of the digital camera we find ourselves snapping them like there is no tomorrow. Millions of pixels stored on something the size of your thumbnail... prints available in just one hour. It wasn't always this simple.

Though often considered an art, photography has historically been all chemistry. The first commercialized photographic imaging technique, the daguerreotype, consisted of a copper plate, coated in silver and then exposed to iodine vapor.

Once the plate had been exposed to light (and we are talking exposures on the order of minutes - far longer than the 1/100 of a second our cameras do today) the image was rendered with mercury vapor and made permanent with a salt mixture. That's a lot of chemistry right there.

Exposing the polished Silver coating to iodine vapor produces the following reaction:

2 Ag + I2 --> 2 AgI

The layer of AgI is light sensitive. Exposure to light produces the following reaction:

AgI + h? --> Ag + I

So the portions of the plate exposed to light consist of Ag, the ones unexposed consist of AgI.

Exposing the plate at this point to mercury vapor causes an amalgam to form in the portions exposed to light:

Ag + Hg --> Ag(Hg)

The last step, the water and salt mixture wash, removes the unexposed AgI:

AgI + 2S2O32- --> [Ag(S2O32-)2]3- + I-Recently Wired magazine had a great article ("History Exposed" Aug 2010) about a series of daguerreotypes taken in 1848 along the Cincinnati waterfront. The daguerreotypes are not only beautiful, but have preserved a moment in history and offer the present a glimpse into what life was like in the city in the middle of the 19th century with amazing detail (far exceeding that of the most sophisticated digital camera on the market today). Some of these images can be viewed here.

Most modern black and white prints are gelatin silver prints - where silver halide salt crystals are suspended in a thin gelatin layer (both film and paper). These crystals are the reason why some images can appear grainy (larger crystals, higher film ISO, more light sensitivity). Daguerreotypes don't have this issue because the surface of the plate is pure and light exposure is decided by each individual molecule as opposed to a whole grouping of molecules.

Print by author made using the gum bichromate process

After the daguerreotype, countless new methods for capturing and preserving images came to light: salted paper prints, Wet plates, dry plates, cyanotypes, albumen prints and gum bichromate prints just to name a few.

The gum bichromate process (also known as the gum dichromate process) is actually pretty simple to perform. It requires a mixture of Potassium Dichromate solution, gum Arabic and pigment to be brushed onto a paper and dried. It is simple to make a contact print from a large format negative: place the negative on top of the light sensitive paper and lay it out in the sun for approx 20 minutes.

The sunlight causes the exposed emulsion (the bichromate specifically) to undergo a redox reaction which causes the gum Arabic to cross-link and become insoluble. The unexposed emulsion rinses off with water .

Though many people have made the switch to digital to preserve their memories of family and friends, some artists and hobbyists still use some of the older techniques, continuing to use them for the beauty and chemistry of it all.

Thoughts? Is anyone out there a photographer, digital or traditional?

(daguerreotype photo)
Merritt, M. Photographic Processes. Feb 2001.
Chemistry of Photography.


Robert S's picture

Good stuff. I think these methods are interesting and allow for more of the &quot;art&quot; of photography to come out. But since access to a dark room is pretty limiting, I stick to the digital format for now. You might be interested that Brain May (you may recognize him as a noted physicist or the author of &quot;We Will Rock You&quot;) recently published a book of stereographs from the 1850s. These are 3D photos that you view through special glasses. <a href="" rel="nofollow"></a>

ehorahan's picture

Thanks Robert! I&#039;ve actually seen a whole bunch of stereographs and the type of camera they are shot on - its really interesting stuff! I am not sure I&#039;ve heard of that book - I&#039;ll have to check it out. Thanks for the tip! Yes, my lack of access to a dark room has also relgated me to the digital world. The gum bichromate process doesn&#039;t require a darkroom to perform, but it does require a caustic chemical which some people may not want around the house.

RGCook's picture

The photos are stunning. The link talks in terms of billions of pixels. And I thought my 5 megapixel macro mode shot of a lizard sitting on the trash can was a masterpiece. Has anyone else noticed that the transition from analog to digital (I say this in broad terms, not just related to photos) has resulted in a decided step back in performance. I mean, digital TV has bandwidth and image quality issues. Same for radio to some extent. Streaming video over the internet is not exactly efficient and a high-quality mkv can&#039;t match up to a decent DVD with upscaling. I think we are in the era of digital transition. We need an order of magnitude increase in bandwith to get us back to 1984. Back to the future I guess, only in HD! HA

Robert S's picture

Completely agree, some of the old methods are going to stick around for those interested in the highest quality. Vinyl has been making a comeback in music, I think eventually the same will happen with pictures. The majority will be digital since it is so easy, portable, fast, and relatively good. But there will be a market for quality.

ehorahan's picture

I share your sentiments, gentlemen. I think though that sometimes its not the quality that makes the difference but the feel of the technology. I do prefer records and part of it is that I can hold it in my hands and can see where the song was recorded and the number of grooves etc etc... the snap crackle and pop add character, in my opinion. Its hard to hold an mp3 file in your hands, and having your computer play it is not as satisfying as placing the needle on the record. Same with photography. Digital cameras have almost leveled the playing field in some respects. It has taken away the need to consciously adjust aperture and shutter speed to obtain the desired effect or manually advance the film. There is something about being an integral part in a production (playing a record, taking a photo) that is truely satisfying.