hello all. new here. have peeked for years but never brave enough to stand up and be counted.

i do largish paintings (30×40) on board. i am colorblind so i build my color slowly with light oil washes until the temperature feels right. the paintings i am doing now explore the range of sepia colors and i am underpainting with a dilute raw sienna. i have been trying to premix a slurry that will one coat the whole board. i have been using galkyd lite, turpentine and paint. it works but barely. not only do i guess wrong about the amount and my remix is darker or lighter, but sometimes the pigment striates. i would love to figure out how to premix a reliable quantity because i run through a lot of it. the galkyd has a sheen to it i don’t really like. its overly reflective to my eye so i thin more with turpentine and the paint gets weak. i have a large glass ash tray from yesteryear i dump it all in and smush it around with an old brush. also i work flat (the washes run) so it needs to dry pretty quick or every spec of dust and flying insect gets included in the painting. would love your thoughts. thank you.