Hi Tony
I did not really elaborate my problem, in my mix of 431 Rutland it is composed of 46% of white, 47% of black, 6% of blue and 0.25% of red for a quantity of 300 gram.
the problem was that at the exit of the oven the gray was brilliant, after all verification I found the problem is the flash that was too strong.
I reduced the flash time and the color is staying mat.
I went from 4 seconds to 2.8 seconds, the logo still has 10 '' x 15 ''
Thank you for your response Tony!
Michel