Ambluetype: the blue ambrotype


Heuristic moment in discovery can be ignited by several occasions. One of them is serendipity: not only chance, but a series of fact randomly happening, which can however be linked together by a hypothesis to be verified in its effectiveness and reliability – this is the scientific facet of this thing. Something has gone this way, while I was making wet plate collodion negatives by iodine intensification. Something has gone wrong, blocking the intensification and preventing the plate from building enough density. The tone range of the image was ok but with a strange green-yellowish colour because of the iodine kept by the collodion film. Trying to scan by transmission the plate – that is to check its behaviour as a negative – I’ve found it useless, and so I’ve tried to use it as an ambrotype, but – as soon as I have placed it over a black surface – the color did changed to a dull blue-grey, pleasant but lacking contrast and brightness. More: the unevenness of the iodine treatment leaved some grey-brownish areas, really unpleasant. This image is published here (flatiron, spectacles and watch).

first ambluetype lores second ambluetype lores

Strange things happen in altprocesses, so I didn’t pay too much attention and tried another shot (see on the left: wooden camera, lenses and glasses). Making the same error, I obtained the same result, and the error was that: I pushed too much the iodine intensification, the excess of iodine hampering the redevelopment, which needs instead an excess of silver nitrate. A blue gloomy positive was made, lacking however bright tones in the highlights and contrast; there were still something to do. And I tried a new fixation bath.

I knew from Towler’s treatise on photography (1875) that this stage I did obtained in my plate was still soluble in hypo, and I dipped the plate into my Thyosulphate bath. In a fistful of seconds the image was quite disappeared, going however through a process of clearing which gave a bright and sharp aspect of tones, gaining strength and saturation in colour, now bright cyan in reflected light against a black background. The only thing to do was to lower the concentration of Hypo or test other fixers, for the optimal effect.

How it works: chemical and physical basis

Giving for acquired the chemical basis of wet plate collodion, a picture has to be produced until the stage of development, according to standard procedure. It is better preferred to start with a more dense plate than that required to produced a good ambrotype, that is, shot as to produce a negative. In fact the process adds translucency to the silver deposit, and the fixing bath lowers consistently the density.

At this stage you will be with a bright ambrotype, not thin like an ambrotype but not enough dense to be effectively printed, and it must be intensified. The intensification can follow three paths. One is sunlight intensification. The other requires iodine depositing followed by pyrogallic redevelopment, and the third is copper intensification.

The second method is effective and gives consistent results, because you have the visual control upon density, which can be raised to extremely high levels. This is why this methods gained popularity in collodion era, and one of the best descriptions of old treatises of photography I think it is that of James Towler, in his “The Silver Sunbeam”, published in 1875[1]

Towler’s words, who wrote these paragraph to explain the process of iodine intensification, are perhaps the best explanation of what happens when you put a iodine excess over a freshly developed plate:

From my preceding remarks it is supposed that the developed image consists of reduced silver, or an altered salt of silver very different from any with which we are acquainted; there is no more iodid or nitrate of silver; these have been removed in the fixing and washing. Now in order to restore the partially developed image to the chemical condition requisite for the recommencement of the development, a solution of iodine in iodide of potassium, or a dilute solution of tincture of iodine, is flowed over the plate, and kept in motion over the image in order to preserve uniformity of ation. The iodine thus coming in contact with the silver enters in combination with this metal and forma a new and thicker deposit of iodide and silver with all the gradation of opacity of the image, and not a uniform film of deposit. The solution of iodine on the collodion loses color all the while; but the collodion filmassumes at first a grayish anf then a yellowish-gray hue. Even at this stage there is much more opacity in the shadows of the picture than before, and the negative by this proceeding may probably be dense enough; if not, proceed to the second stage. The first stage is the depositing stage; the second, the reducing or developing stage proper; and yet this deposit of the first stage is a chemical combination of iodine and silver which is now soluble in the fixing solutions, and before it was not. By this process of depositing and fixing, and by regulating the quantity of iodine solution, a negative which is too opaque may be rendered more transparent and less dense ad libitum. Osborne has availed himself of this property to clarify his negatives for obtaining enlarged positives in the solar camera.

If you push the iodine intensification, by increasing the concentration of iodine and by extending the time of treatment, the iodine excess enters the collodion film and builds a thick layer of Silver Iodide by reaction with the silver contained in the image, and “with all the gradation of the image and not as a uniform layer” as Towler wrote. The aim is to combine with iodine all the silver particles in your collodion. Silver iodine has replaced the metallic silver. Some potassium iodide is formed because potassium is part of Tincture of iodine formula[2].ambluetype - stadio giallo lowlowres

Potassium iodide doesn’t follow the gradation of the image, because isn’t related to the presence of silver. It forms, instead, a diffuse layer responsible of the opacity of the film, which need to be cleared. Also the veiling of the image, if any exists, being made of reduced silver, is now converted into iodide of silver. Either the film of potassium iodide (insoluble in water, but easily washed by the fixer) or the thin deposit of silver iodide in areas of veiling, are dissolved by the second fixing bath, who however can attack also the silver iodide by which the image is made. Acting as a clearer/reducer at one side, it jeopardize the image at the other. This is why the second fixing bath must be a very diluted one, and visual control must be hold with care to arrest the fixing at the desired stage.

The outcome is a yellow deposit of silver iodide in your piroxyline layer with the gradation of the image, clear and sharp, without fog, and which you can also further reduce, at any extent. Bright and deep yellow in reflected light over a white sheet, is seen clue against a black background because the light seeps through and is reflected to the eye, after being refracted by the iodine layer, that behaves like a filter, leaving only the complementary color.


What do you need

  • Photographic collodion for negatives (you can us however standard positive formula)
  • Ferrous sulphate developer for negatives (or dilute 1:2 or 1:3 your developer for positives)
  • Thyosulphate first bath: 30% (300 g Hypo in 1000 ml H2O)
  • Strong diluted iodine tincture: you can purchase iodine tincture and dilute it 5% (25 ml, adding distilled water to make 500 ml). The percentage given is far from a rule: you can add tincture to distilled water until you have reached the right color. A stronger solution will complete the process in a shorter time.
  • Thyosuphate second bath: 3% (30 g Hypo in 1000 ml H2O)



prepare, shot and develop a wet plate collodion as you were doing a negative. So use negative formulas for collodion and developer, expose longer than for an ambrotype, develop longer to build enough density.


fix in thyosulphate 15-30%, and wash carefully, for 10 minutes (usual washing time for hypo should be 30 minutes, but you must wash further after the second fix bath, so you can shorten this first step)


flow a strong solution od iodine tincture. Stay over a tray, or use a pyrex lasagna tray, which allows you to observe the color of the plate, and to maintain the plate submerged with a relative few amount of iodine solution, keeping in movement until the process is completed. The process wil take a few minutes. The image starts to become yellowish, and then bright yellow in the highlights. Owing to the amount and concentration of iodine solution, it will lose density and clears during the process, but doesn’t become colorless. The plate instead, becomes on time uniformly yellow, the last areas being the thickest. You don’t run the risk of over treatment. Look for any unevenness, because insufficiently treated areas can attain a brown-black color, resembling in the finished work a sabattier-like effect, as in one of the enclosed reproduction ("Why so angry?") can be seen near the eyes of the fishes.


wash carefully the plate until the water stops beading like over a grease surface and flows evenly over the plate.


if you can, expose the plate to UV light (lamp, sun) for a minute: this increase density and raise contrast and acutance. Now the image is yellow, but a bit opaque and greenish if watched against a black surface


dip the plate in a black tray filled with 3% hypo second bath. Watch carefully while moving the plate. The image will clear and gains in saturation, becoming a pale cyan. It will take 20-30 seconds. After this time the fixer starts to quickly reduce the image and a water filled with tray must be available to stop the fixing


wash in running water or change frequently the bath, for 30-40 minutes, dry the plate and sandarac varnish it as usually. Black paint the back of the glass as for an ambrotype


[1] Available here

[2] Iodine is usually 7% elemental iodine, along with 5% potassium iodide (or sodium iodide), dissolved in a mixture of ethanol and water.

The role of iodide and water in the solution is to increase the solubility of the elemental iodine, by turning it to the soluble triiodide anion I3. However, since iodine has moderate solubility in ethanol, it is also assisted by this solvent directly. Potassium iodide is added because it allows to dissolve a more quantity of Iodium