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Clues From Echague. One.

 My own Direct Carbon technique is an extensive modification of the following in which I do not use Gum of any kind. Gum dissolves far too readily in Dichromate when dipping and will just float the pigment away before it has a chance to remain on the surface of the gelatine. I seem to remember that  in Art's process he incorporates the sensitizer in the one coat pigment layer. This does work but obviously does not follow the clues given by Echague.
There are many ways to skin a cat, although I would never do that. They are far too helpful to me in keeping my blood pressure down.
You will see there is a great similarity to the Gum process using what appears to be a sizing coating which seems to be an important part of the successful making of the image  in the Fresson formula. 
Based on the translation of an article in '' Arte Fotografico'' by Jose Ortiz Echague on Fresson Printing. Around 1950
''The methods of Direct Carbon are those are those in which the image is obtained directly on the original paper without the necessity of being transfered once or twice onto other supports, as occurs with carbon papers for double or single transfers.
In either process the paper is coated with a layer of gelatine but which  supports,  only in the Direct Carbon process, a layer of pigment dissolved in a mucilage, instead of being incorporated in the same base gelatine as occurs in the Carbon Transfer process.
Here stands out the fundamental difference between Direct Carbon and Carbon Transfer. In the transfer method the undissolved gelatine, more or less, makes an impermeable  outer layer, and it is then necessary to invert this to dissolve the pigment confined beneath to make the image visible
In the direct carbon process the pigmented layer located on the surface of the gelatine penetrates only superficially into the interior of it, and so can be attacked from the outside without inversion onto another support. This abrasion of the gelatine/pigment  in Direct Carbon requires a more energetic medium than just the dissolving action of a water bath which alone would be insufficient in developing/ clearing the image.
So, to recap.The paper forDirect Carbon is made of a thin layer which is generally gelatine;  on this layer is coated the pigment dissolved in a vehicle such as Gum Arabic, Tragacanth Gum, Lichen, Agar-Agar etc.,  but the base coating is always formed of a thin layer of gelatine in direct contact with the paper support.
 The result of this way of preparing the paper, for one thing, is the various qualities that can be obtained according to the proportions of gelatine and gum  muclage used and also the thickness of the pigmented surface layer and the extent to which it penetrates into the base layer when development takes place.
The most usual commercial papers are the brands, ''Fresson'', ''Artigue'', and ''Hochheimer''. Their manufacture is a secret of their makers and certain of them have disappeared with their originators. 
Sensitization is by dipping the prepared and dried paper in a 1% to 4% Pottassium Bichromate solution.
Enjoy, already. 
John- Photographist - London - UK