Digital BW, The Print

I have Hydrocote and a Meyer rod and have seen the effect this has on 
my UT-1 prints on PhotoRag. An obvious difference is the increase in 
contrast and (even though I can't measure it via densitometer) the 
increase in Dmax.

More recently I read with interest the threads on spray coatings and 
ended up buying a can of Lyson Print Guard, which is supposed to be 
identical to Clearshield. I expected this to have a similar effect in 
terms of increasing contrast and Dmax, but was surprised to see that 
3 coats sprayed onto a print seems to yield no visible difference at 
all with an unsprayed print.

Did I miss something? Is the rationale for using the spray coatings 
UV protection and print longevity only, or is it also for increasing 
Dmax?

Best,

Dave