These are a Maibec cedar shingle treated with a bleaching oil

Is the bleaching oil added at factory or on site at time of installation? Also do you know how this will weather over time? Thank you!

they come predipped from the manufacturer. The shingles will weather gray, but sometimes over time dark gray, if they do not get a lot of sun or are damp for extended periods of time because of shade or sometimes brown if over exposed to weather conditions. It may not weather uniformly over a few years. One way to keep some uniformity over time is to have it pressure washed and if needed reapply the bleaching oil on site.