When it comes to 70-100 year old weathered wood, there is no such thing as "straight". Even the wood that looks straight is not straight by new wood standards. Granted, some wood that twists like a roller coaster spiral is too far gone to use, but most is usable. It just takes a lot more work.
The first step, once the wood has been removed from the structure, is to remove all nails. The next step is a cleaning process to remove all dirt that decades worth of weathering can bring. The boards then have to be sorted and cut into strips that are acceptable to be used in the frames. This also means discarding any parts that are too weathered and rotted to be used.
Now...we have arrived to a point of where most frame makers that construct frames from mass produced frame molding sold in bundles begin their day...kind of. The faux barnwood molding that most rustic frames are manufactured from is cheap, thin, and flimsy pine boards that is mass-produced just like the wall molding you buy in the hardware store and painted to mimick weathered wood. But...it has one advantage! It's straight.
You want to make a frame maker's life miserable? Give them slightly warped wood. The word challenging comes to mind. Although a board may look straight to an average person, in the precise business of frame making, one degree off on a cut completely compromises the craftsmanship of the frame. It's much easier to grab a straight stick of molding off the rack, but, as with most things that are easy, it will never compare to the authentic nature of real antique wood.
There are times that as many as six clamps might be used at once in the manufacture of your frame, along with techniques to make the wood relax. If you've ever wondered why this level of custom frame takes longer to manufacture or has a higher price point, this is why. Even though the cost is higher, the value added amount in the product is 300% - 400% more than what a customer receives in the cheap, faux rustic frames.
There is no substitute for the real thing, and when a customer hangs a real century old wood frame next to a faux rustic frame, the stark contrast of the two can be overwhelming. The end result from all of that work can be seen in photo above in the natural oak frame. A beautiful antique frame from an old, dirty, warped board that looked to be completely unusable.