In my trad days, if you saw me in the early years, you would wonder what the heck I was upto. After I cleaned the windows I use to stand or squat to look at the windows from all sort of angles to make sure no marks were left.
The worst was leaded windows, scrimming them. After checking from two different angles I thought I had cracked the technique ut then that final different check showed the smears.
I hated leaded windows, even giving them a quick spray and scrimming I hated. In the end I found a great dilution mix of blue titan, mopped the windows and used a 14 inch channel that allowed most pressure for glasd contact to blade off and then a light scrimming polished it up lovely. Or should i say, detailed them brilliantly