The Roncarolo system required a camera capable of recording two panchromatic negatives (which became three or four in subsequent patents) through the use of a beam splitter and red and green filters.
The chromatic information registered on the two or three negatives thus obtained had to be recomposed through printing on a single positive, in turn to be submitted to a coloring process. Naturally, the separation negatives being in black and white, the development operations were quite similar to those foreseen for any black and white panchromatic film. In the two-color version, the printing took place simultaneously on one film strip with two layers of emulsion, one on each side: a comb-type recording system ensured the perfect superimposition of the two negatives. The positive thus obtained was then colored in red on one side and in green on the other by having it glide over two consecutive dye baths. The dyes used were complementary to the shooting filters, in order to return to the natural color of the subject initially filmed (the first patent also provided an alternative system in which the coloring was performed by a series of brushes with a spatula connected to a tank).
With the transition to three colors the procedure didn’t change substantially: it became necessary to apply a further layer of emulsion and proceed to a third layer of dye, using the same apparatus. Roncarolo’s research to perfect this phase of the process continued until the invention of two methods of matrix printing, similar to the type adopted by Technicolor. In addition to a similar procedure to that of the US company, based on the use of the three selection negatives for printing the matrices on a separate support, the Milanese inventor patented a system that allowed the same negatives to be directly transformed into matrices, in order to avoid an extra step in the already complex laboratory operations and also to save money.
In theory, a potential producer interested in making a color film with the Roncarolo system could thus have chosen which of the three printing methods to use, based on their own economic needs, or the desired quality.

Pierotti, Federico (2016): Un’archeologia del colore nel cinema italiano. Dal Technicolor ad Antonioni. Pisa: Edizioni ETS, p. 100-101. (In Italian)
Translated and adapted by Noemi Daugaard, SNSF Film Colors. Technologies, Cultures, Institutions.

Original Technical Papers and Primary Sources

Roncarolo, Emilio (1938): La cinematografia a colori e il sistema Emilio Roncarolo. Roma: Sallustiana. (In Italian)

Secondary Sources

Pierotti, Federico (2016): Un’archeologia del colore nel cinema italiano. Dal Technicolor ad Antonioni. Pisa: Edizioni ETS, on pp. 64–69 View Quote and on pp. 100–101. (in Italian) View Quote

Sainati, A. (2003): L’esperimento della Rivista Luce. In: Bianco e Nero, 1–3, pp. 63–68. (In Italian)