Scotch Guard, Camp Dry, others of different name will get you decent water repellency. They will however wash out. Reapplying is not a problem, but becomes time consuming and somewhat expensive. I have tried using other peoples "rejuvinating" waxes on an old hunting jacket, it didn't work. If you really want it water repellant. Hang it on the north side of a building so the sun does not hit it and paint it with boiled linseed oil. Takes a long time to dry and really should have a second coat but when your done, you chould have as near waterproof as you can get with cotton. One other option I can think of is using "Canvac" its used to recoat tents. I'm not sure of the spelling but that's close. Should be able to find it on line or places selling quality canvas tents.
I just waxed a new skin out leather fringe jacket. I uses Sno-Seal that was recommened on this forum. It is bees wax and it worked great. I have not tried it on cotten, but if you would like I will give it a try. The leather jacket that I did was lamb with the shin side out. It had a natural finish. The Sno-Seal darkend it a little. It now looks like it has been worn for several years. I would think that using it on cotten would give you a coat that is like an english Barbor coat. They are made from waxed cotten. When I get a duster, I will use the Sno-seal on it.
If it leather you are woried about,I would use PURE NEETSFOOT OIL,it may discolor the leather a bit,but will soak in and do a good job on the leather. It can be purchased at just about any leather store,or leather shop. King
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