I bought some pine the other day and it has this yellow stain on the end:
I sanded off the yellow before using the pine, but now I wonder what it was and if that was the right thing to do. So what exactly is the yellow stain on the endgrain of the pine I bought?
The paint isn't only used to identify the wood boards by lumber yards, but it's also used to seal of the end grain to slow down the drying process.
Because exposed pores or tracheids on the end-grain surfaces promote too-rapid drying and result in checks, it is wise to coat the ends of boards to slow the moisture loss from the end grain. Almost any impervious material will do. Wet wood can receive a primer of acrylic latex paint first. Aluminum paint, oil paint even melted paraffin will seal the wood. Coat the ends as soon as possible after sawing to minimize end checks. In wood such as beech, checking can begin in a matter of hours. Oak is also quite susceptible. Once checking occurs, the damage is done.
Source: Christian Becksvoort (2013), With the grain : A craftsman's Guide to Understanding Wood, p.99
Lumber mills mark their boards with different colors to quickly identify them. Generally you'd cut off the end of a board after ripping it to get a nice square end. Sanding works too but is a lot of work.
