I get asked this a lot. It's really not hard to do. The main thing is the lumber I use is barnwood that has weathered for decades. After ripping into strips (13) I plane one side for thickness. Nonplaning the side I want to keep the weathering scars on. After joining together with strips vertically on the backside, I use acrylic or latex paint watered way way way down. I paint the strips until the saturation that I want is reached. Then paint the blue field, using more black or charcoal than actual blue. Then I might use full strength colors to just highlight certain spots. But, I would say that a propane torch is the best aging tool I use.
From ripping the boards to glueing on the stars and building a frame around it takes me an hr maybe. Then I use. Couple very heavy coats of poly.
Chad
That is great info. I recently made a large (5×9 foot) wood flag and after seeing yours I will try the antiquing process. Too late for the watered down paint but I can torch it and maybe brush on some stain. Thanks!