Richard asked me to write a short description of Edouard Baldus' calotype process, so here it comes.
The way I do it is pretty much as described in this book.
It contains an English translation of a description of his process that Baldus published in 1852. As my French is very poor I haven't tried to track down the original text, and especially as there are not any problems at all with the English description I am happy following it.
First Operation Melt 10 g of gelatin in 500 g of distilled water. Add 5 g of potassium iodide to this and mix thoroughly. Then slowly add 25 g of the acetonitrate described in second operation while slowly stirring. Pour the yellow solution into a tray kept warm in a water bath and float the papers for six to ten minutes each depending on their thickness. Remove the paper and hang it to dry. When the papers are dry mix a solution of 100 g distilled water and 1 g potassium iodide. Soak the papers one and one in this solution for six to ten minutes and then hang them to dry again. Store the papers. The gelatin/potassium iodide/acetonitrate solution can be saved and reused. It seems to keep for a very long time, my batch made almost a year ago still works.
Second Operation Mix acetonitrate from 100 g of distilled water, 6 g silver nitrate and 12 g glacial acetic acid. Pour this into a tray and float the papers with the yellow side down until the entire surface of the paper assumes a uniform hue. This should take five to six minutes. Then either place the paper on a sheet of glass and put in the plate holder if it should be used wet. If it is to be used dry wash it rapidly in distilled water and hang it to dry.
Third Operation Put the plate holder in a camera and expose.
Fourth Operation Prepare a saturated solution of gallic acid and float the paper picture side down on it. An instant later turn the paper over so both sides are soaked. Leave until fully developed. If needed a few drops of acetonitrate can be added. However, Baldus states that a good negative should be able to be completed in gallic acid alone.
Fifth Operation When the image is fully developed wash it in filtered water for up to fifteen minutes. Then prepare a solution of 100 g distilled water and 3 g potassium bromide and plunge the paper into it. If the solution takes on a greenish tint the paper has not been sufficiently cleansed in the water. If so, renew the bromide bath. Leave the paper in the bath for at least half an hour. Wash the paper carefully in several water baths.
As an alternative the paper can be fixed with a solution made of 100 g water and 7 g of sodium thiosulphate.
Or as a last alternative, use a solution of saturated sodium chloride.
The washing procedure is the same for the last two as for the first alternative.
The second, fourth and fifth operations must be performed in a darkroom by red light.
Then a few observations and modifications from me: The last potassium iodide bath from first operation is done to increase the sensitivity of the papers according to Baldus. It makes a very small difference for dry papers, and it is only for that type I have tried to leave the bath out. See a comparative scan here:
where only the right part is run through the second bath. The test is made by cutting the same iodized paper in two halves and giving one of them the extra bath. They were then sensitized together for the same time, exposed together in the same holder and developed and fixed for the same time in the same baths.
For dry papers the whole paper can be soaked in the acetonitrate during second operation. I then wash it in two baths of distilled water to really minimize the risk of fogging. I save the first water bath and use it during development as it contains enough silver to intensify the calotypes if needed. I save and reuse the acetonitrate and I replenish it when needed. For me a lot of organic matter from the gelatine ends up in the bath so I store it with a lot of kaolin and filter well before each new use. Some sunning now and then is also a good thing to keep it in order. Wet papers are not possible to mount between two sheets of glass, I get a lot of disturbing bubbles from the gelatine that spoils the picture.
When developing dry papers it can take 20-30 minutes before the image starts to show, and I often have to leave the paper in the bath for two or three hours. Wet papers behave more like Baldus described them.
At EV12 f8 I expose dry papers for four minutes and wet for about two.
I can keep Beinfang papers for 5-6 days after sensitization. The batch of Canson marker paper I have must be acidified before I use it, otherwise it will blacken during development. And still it will only keep for 12-18 hours before it starts to fog.
I have only fixed in hypo, so I have no idea how the potassium bromide or the salt fixing works. It is on my list of things to try...
Then a few transmissive scans of three of my calotypes, made as descibed above on dry Canson marker paper, to give you an idea on how the calotypes turn out and how they print:
All the prints are made from unwaxed calotypes as I am not very happy with the look Canson gets after waxing.