|Left: New Bottle, Right: Aged Bottle|
Rather than achieve an aged look with paint, I tried to seasoned the outside of the bottles as I do cast iron cookware. This experiment was very successful. Seasoning cookware requires applying thin layers of oil and baking the cookware between the layers to create a hard, protective outer surface.
Caveat: There are products and techniques to paint on glass that require the glass to be heated to a temperature in excess of 300 degrees Fahrenheit. This can be successfully done when proper care is taken to ensure that glass is not subjected to quick changes in temperature. Be sure to start with undamaged glass--no cracks or chips please. Be sure to place glass in a COOL oven, allowing the temperature of the glass to rise as the oven temperature rises. Also make sure to turn off the oven with the glass inside, allowing it to cool as the oven cools. Do not attempt to change the temperature of your glass quickly because that is how breakage happens.
I used flaxseed oil on my bottles because it is a "drying oil" which would give a hard finish while still being food safe. It gave a yellowish sheen that was exactly what I had been looking for. Since organic flaxseed oil is what I'm already using to season pans, I thought it was ideal. My first experiment was with canola oil which gave the right sheen but was sticky. So do yourself a favor and use a drying oil. If you are simply aging bottles for display, you can use linseed oil instead. To read a bit more about the chemistry of seasoning surfaces with oil, check out this post on Sheryl Canter's blog.
Before seasoning the bottles, I wiped down the clean bottles with rubbing alcohol and let them dry. Next, I applied an extremely thin layer of my organic flaxseed oil to the outside of a clean dry bottles. Then I wiped it off which left behind a very thin, almost imperceptible layer. I placed the bottles on a foil-lined pan in a cool oven. Then I turned the oven on to 350 degrees. I baked them for about an hour and a half before turning off the oven and allowing the glass to cool down while inside the oven. Once the bottles were cool, I repeated the process to build up a few layers. It does take some time but the process was easy and the results were worth it.
Be aware that any pattern of oil streaks you leave on the glass will show. Also, too thick of a layer will cause the hot oil to drip down the bottle, creating dark yellow droplets. So make sure you create only the slightest haze on the surface when you wipe away the oil. I experimented with several glass beer bottles in the pursuit of the right technique for applying the oil so you might consider some trial bottles before moving on to your favorite one.
The aged bottle pictured has three layers of oil.