Mix 1/3 cup of Modge Podge with 1 cup of water until well combined. Add as much gel food coloring as you would like to achieve the desired color. Remember that the glass will be several shades lighter than your MP mixture. Stir the food coloring in very well.
I used a liquid measuring cup for the mixing, so it was easy to pour the mixture into the bottles. Pour about 1/4 to 1/2 cup of the mixture into the first clean and dry glass bottle. Swirl the liquid mixture around the inside of the bottle until ALL inside areas are coated with color. Pour extra color mixture back into the liquid measuring cup. Repeat this process with all of your glass containers.
Turn all containers upside down on a layer of newspaper or paper towels and allow to drain for five minutes. Next, set containers upright to allow any liquid that did not drain to return to the bottom of each container. Allow the containers to set for at least 1 hour or you will have ugly streaks in your finished product. You can see several in mine.
Remove the top rack from your oven. Place the bottles on the bottom rack. (Smaller bottles can be placed on a cookie sheet.) Set oven to 180 degrees. When oven has preheated with bottles inside, set your timer for 20 minutes and allow the bottles to "bake" until the timer reaches zero.
Carefully remove the VERY hot bottles and set them on a heat-safe surface to cool. If you want the color to be darker, repeat this process once the glass has cooled COMPLETELY.
After a couple of days, I decided to try a few more colors. I bought both of these pieces at The Dollar Tree.