QTR-Quadtone RIP

Hello chaps,

I'm entering the dance of linearization process and catch almost all 
the subtilities involved in the game of creating a new curve..

*deleting shadow, highlights and linearization data
*ink limit (60% in my case)
*black correspondance of light black at ink limit (22,5%)
*Print of the 21 scale wedge
*Scan the patch with a fladbed scanner and work it with PS in lab 
mode
*Creating the "pre linearization" PS curve is almost OK, but it led 
to somme limitations explained below:

The paper (Arches watercolor infinity) has a creamy white which 
correspond to 7% black. The darkest patches level up to 85% black 
for the theoretical 90-95-100%. The linearization process works 
well, but only between 10 and 85%

Do you have any piece of info on how to get back these cutted parts 
of the histogram? 

Thanks for yous answers,

Digital_joshua