I paint in encaustic (beeswax and copal-resin pigmented paint). I have not done any fabric coating for utilitarian use like sandwich bags, but it is my desire to do this that brought me to this discussion (via google search). Here are my comments based on what I know from using and working with beeswax as an artist.
Beeswax melts at 140*F, and is flammable at 212*F, so DO NOT try to heat fabric in the oven until excess wax flows out -- you will have a hellacious oven and house fire.
Water and wax will NOT mix into an emulsion, so you can't heat, mix and dip, as one person suggested, unles you use an emulsiant like lye-- at whcih point you are making soap, and will loose the water-barrier properties of beeswax that you are seeking in a lunch wrap.
Don't mix beeswax with parrifin or turpintine, as neither are food safe (parrifin is a petroleum byproduct)
Beeswax is ralatively supple at warm temps, but will become brittlel at cold temps. Therfore if you wrap frozen or cold cold sandwiches, or plan to pack lunch with a cold pack (for food safety), or put luiunch into the refigerator, you may want to make the beeswax more supple so you don't dine on dandruff sized flakes.
If you treat your fabric before sewing it, you will have to dedicate a sewing machine to this (it will have a short short life), or sew by hand.
Based on my experience, this is what I plan to do. I will post my results if and when I ever get around to doing the project.
I will create wraps, rather than bags, and prehem organic cotton or hemp squares measuring about 20 " across the diagonal, with tying tape/ribbon attached to the sqares at one corner and at an approriate off-center mark on the otside of the wrap. I'm not very good at using patterns, my machine is broken, and I sew well by hand.
To treat fabric I will melt and mix together 1 part oil to 3-4 parts beeeswax. I will use a food--grade highly filtered oil -- not sure what kind, but certainly not a virgin olive oil.... something very filtered, light and pure. Remember, oil will b/c rancid over time... these cloths may last for a year of so, but I plan on having to remake these on an annual basis or abandon being the most pc green-gal in the hood.
streach fabric on a frame, and point with melted wax-oil mix, making sure to work into the fibers.
After cooling, I will place between generous layers of CLEAN newsprint paper (no print) and iron with a low heat to remove excess oil. You can buy clean newsprint at art stores. The inks used on newspapers is icky... not foodsafe.
Hand-launder in cool (not cold) water with a light Dr. Bronners squirt before use.
After each use, hand-launder aind hang dry n a similar fashon.
WOW that's a lot of work to do this... Maybe I'll just continue to buy wax sandwich bags. I get a brand called Western Family -- they are brown recycled wax paper bags. Love them. We try to reuse them at least once if they don't get too wrinkled.
IF I EVER try making these bags, I will post my results. If anyone else tried this, I'd love to konwo yoru experience.
Sara