Ok Pat lets see. Formaldehyde is a colorless odorless gas that is the byproduct of various things. From what I can remember from basic chemistry a LONG time ago its chemical designation is HCHO, me thinks. Please keep in mind that chemistry is not my field and I prefer ta stay non-scientific. Iam a primitive archer. Well, some foks would say just plain primitive !
Most would be familiar with wood smoke, it has the formaldehyde compound in it. Its a resin and binder. Interestin, could it help bind the resins an polymers in wood ? It can produce irritation to the eyes, mucous membranes, upper respiratory system etc. Over exposure can cause serious health problems. The medical field used it extensively in past years but not so much today. Hmm........... vapor barrier ! I would prefer ta call it vapor retarder. Water (vapor ) moves in an out of all porous products as we know. Wood is one of those. Most smoke a hide after ya brain tan it. A byproduct of this process among others, is that the formaldehyde in the smoke waterproofs (somewhat ), softens and has excellent bug retardent properties. When I was a lad the elders that taught me ta make bows said ta always build a smudge fire and smoke the wood after ya grease it an bone it hard. Not everytime but once in a while especially in wet weather. The smudge fire had ta be of the wood the bow was so "the spirit of the wood can reenter " Since cultural dictates say ya never question an elder I just accepted it. I always wondered about this and years later bein' a growed up Indian I asked my Grandfather about it. He said " Not good enuf explanation fer ya huh ? " Oops !
"Yes Grandfather good enuf ! "
I know that I have built bows from wood that was not smoked and they had more string follow than those that were smoked. I believe that the formaldahyde helps harden the resins and helps cure the wood. Then the bear grease er hawg grease waterproofs it. One thing I dont like about the various varnishes and urethanes is they stay on the surface . I prefer a penetrant . As the water leaves the wood my impression is that the grease enters and takes the place of the water so the cells dont collapse. Btw formaldehyde is a natural byproduct of human cell activity. The more grease in wood the less water vapor transpiration. As I said Iam not scientific but it appears as I have said in my longtime experience. As far as "spirit of the wood reentering " I will leave ya all ta make that decision fer yerselves as to its veracity or not .
.....bob