The 50 % gum is what I had been using for twenty years before I changed to
Gloy for much of my work. I used, and use, it because I found that it gave
far better results than the thinner gums recommended in the standard text
books.
The 50 % gum gives strong results with fewer coatings. Three coats giving
greater tonal range and realistic subtlety than prints I have been shown,
using thinner gums, using fifteen coatings or more.
I use Gloy now as it needs no preservatives and gives more consistent
results.
When I started, the recommended preservative for gum was mercuric chloride.
As I avoid things that make you dead quickly I only mix enough gum for a
few days work. Admittedly that does not allow one to keep long rows of
ready mixed gum and pigment on the shelf but that has its advantages as
that system tends to produce insipid results.
Terry King