Salvatore,

While sizing is important when looking at staining, pigment choice and how it is dispersed is much more critical. To highlight this, I spent well over 15,000 euros testing and purchasing suitable pigments for use in carbon and gum printing, while my research into finding a suitable sizing for gum printing only cost me about 2000 euros. Comparing staining between various people is difficult since the amount of pigment I used or you used in your emulsion is going to have a huge effect on staining.  Attached is a photo showing my test charts with a color checker chart in the middle for reference, but below is the actual data read with a spectro. I am providing them in Lab values and densities.

Paper white- Lab values (97.5, 0.1, 3.2) CMYK densities (0.02, 0.03, 0.05, 0.03)

Cyan- (97.3, -0.4, 2.70) Density- 0.01 which translates into a 0.00 Difference caused by staining.

Magenta- (97.4, 0.3, 3.1) Density- 0.03 which translates into a 0.00 difference caused by staining.

Yellow- (97.2, -0.5, 4.4) Density- 0.06 which translates into a 0.01 difference caused by staining.

Black- (96.1, -0.2, 4.8) Density- 0.04 which translates into a 0.01difference caused by staining.

Iron Oxide- (96.8, 0.5, 5.4)

The maximum densities for those test charts are Cyan 0.96, Magenta 0.83, Yellow 0.71, and Black 1.23. These densities are enough to make a decent profile, as seen here- https://www.facebook.com/59511578/videos/10103900526231556/, and make a print as seen here- https://youtu.be/83yLFL1Tb7I.

Here’s a link for anyone interested in these pigments- https://thewetprint.com/en/pigments/, they can be purchased at the bottom of that page, but the article is also interesting.

That being said, the search for clean prints goes beyond just sizing and pigments, as there are a number of other factors that will affect staining. For those interested in the pigments, I would like to say that you are probably not going to purchase those pigments, and have your prints look perfect. There's no such thing as a magic bullet in gum and carbon printing. Getting clean prints requires a lot of research as well, but using the right materials will get you on the right track.

Onwards and Upwards,

Calvin

P.S.- I would like to add that I mostly sell the pigments so people, i.e. my students, have access to a quality product.  I wasted thousands of hours struggling when I first started out because I did not have the right materials. It wouldn’t make any sense for me to teach a workshop on how to make a good carbon print, then at the end say, “oh well, you can’t make a print like this since you don’t have the right pigments, sorry.” So in the end I make most of my living teaching, a bit from making and selling prints, some from ebook sales, and so far over the last two years have lost money selling pigments.