Daguerreotype Process
First, some history (sorry but I’m not a historian):
To the right is the first successful photograph called “View from the Window at Le Gras” (circa 1826). 
It was produced by a process called “heliography” or sun drawing in which a pewter plate is coated with a light sensitive substance of asphaltum or bitumen of Judea. The black colored bitumen hardened when exposed to light creating distinctions between light (the shiny pewter plate) and darks (bitumen that remains on the plate). These are the basic elements that combine to form a perceivable image. This heliography, developed by Joseph Nicéphore Niépce, had obvious limitations but he continued to make improvements on the process. Substituting the pewter for silver plates and introducing the use of iodine fumes with the bitumen, positive silver iodine images were made having increased detail.
Partnering with the French chemist and artist Louis Jacques Mandé Daguerre, he was provided with a complete description of Niépce’s process. Using it as a foundation, Daguerre developed what is now known as the daguerreotype process. He discovered that silver iodine (made by fuming the silver plates with iodine as Niépce had been doing) was itself sensitive to light and could be used alone without the bitumen to produce images. He also found that a latent, non visible image on the silver plate could be made visible or developed out by exposure to mercury fumes. However, this fragile layer of silver amalgam particles and silver iodide that sat atop the silver plate could not be made permanent. Meaning the action of light still acted upon it every time it was viewed, darkening the image until it was not visible. For two years Daguerre struggled with ways to “fix” the image until he was finally successful by saturating the image in hot salt water, which was pointed out to him by Sir John Herschel. This cleared the remaining silver iodide that had not been exposed to light, keeping it from continuing to change and darken.
Unfortunately in 1833 Niépce died, before Daguerre had actually made these improvements. The improvements were so drastic that Daguerre felt the two processes had become quite different from each other and had insisted it should be given the name daguerreotype to reflect these differences.
In Paris, 1839, the French government acquired Daguerre’s patent and announced his invention “a gift free to the world”. Although the daguerreotype was not the first photographic image that had been produced, Daguerre is almost always given credit for doing so.
To the right is the first daguerreotype made by Daguerre himself.
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So, what is a daguerreotype… it’s a direct positive image formed by silver amalgam particles that ‘develop’ on the surface of a highly polished sheet of silver after exposure to light. The varying amounts of particles on the surface is what gives the image its tonal range and contrast. The highlights or white areas are visible because the light that falls on the particles are scattered into your eyes. The more silver amalgam particles present on the plate, the more light scattering and the brighter or whiter it appears. The shadows of the image are the areas in which no (or very few) particles have developed and the polished silver surface reflects all light away from your eye appearing very dark. This is why a highly polished surface is required and is also the reason the image reverses to a negative so easily. There is a limited angle at which the daguerreotype can be held to properly reflect light away from your eyes in the shadow areas leaving the image to appear properly as a positive.
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The process consists of:
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- Sanding and Polishing the plate:
- Coating or sensitizing the plate:
- Exposing the plate in the camera:
- Developing the plate over mercury:
- Fixing the plate:
- Gilding the image :
The copper plate will come from the factory with mill marks that are usually 5 to 30 microns thick. These are taken out by using various micron fiber polishing papers and abrasive solutions.
At this point the copper plates are put in the silver plating bath to plate a layer of pure silver onto the surface. Multiple layers are usually needed to ensure an even silver layer on larger plates.
For the clad plate, (thin silver layer mechanically fused to a sheet of copper by pressure) they are ready to be galvanized after micron fiber polishing and sufficient buffing with buckskin. Galvanizing adds a very thin layer of silver over the base silver for an even better daguerreotype surface. This step is applied to the electroplated copper plate as well.
The plate is exposed to iodine fumes from a box that has iodine crystals laying on the bottom. The iodine fumes touch the silvered surface and create a thin layer of silver iodide on the plate. As this silver iodide layer grows, it’s color changes. The different colors that are seen is what determines the how long the plate stays over the iodine fumes. A solid golden yellow with a little bit of rose coming through is a great starting point.
Exposure to bromine fumes is next in a separate fuming box. The exposure to bromine is determined by time tests and not necessarily by color. Bromine makes the plate a lot more sensitive to light, drastically cutting down the camera exposure times from minutes to seconds.
Exposing the daguerreotype plate in the camera is not that much different than ordinary film except that it’s very insensitive to light, resulting in longer than normal exposure times. On sunny days with a lot of light in the studio and a fast lens, the exposure is around 15 to 40 seconds. The head brace is used for portraits just to ensure heads don’t move too much.
The plate is placed in a mercury fume box where it is exposed to hot mercury vapor for about 8min. The mercury acts as a catalyst to develop out the latent image forming a fragile layer of silver amalgam particles that rests on the mirrored surface (mercury is not consumed in the process). These particles are what create the daguerreotype image.
Sodium thiosulfate is used to remove the remaining, unexposed silver iodide.
Gilding the plate with gold chloride is the final step. After the plate is rinsed well with distilled water, a mixture of gold chloride and sodium thiosulfate is poured on the top of the plate. The bottom is then heated with a flame and as the temperature increases to near boiling, there is a chemical reaction that takes place where the gold in the solution transfers with the silver mercury amalgam on the plate.
This gives an increased contrast, deeper and richer tones and also makes it more archival. However, because it’s a relatively expensive step it’s usually reserved for images that are keepers and is an optional step.
Here is a short list of what equipment is needed for making daguerreotypes:
(hot mercury)
- Silver electroplated plates or clad plates
- Iodine and Bromine coating boxes
- Mercury fume/developing box with heater
- Fume hood – this is not optional!
- Sanding materials – Polishing compounds and pads
- Buffing sticks
- Gilding stand
- Spirit lamp
- Camera fitted to hold your plates
- Misc things like fixing trays, gloves, iodine, bromine, sodium thiosulfate, gold chloride, mercury, and a few others.
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Early Daguerreotype Kit with everything one would need to take up daguerreotypy!
