This subject was one of the things I was keeping silent on, only giving out a few hints in my blog. However, Momma Starr and Dr. Lovebug have already let the cat out of the bag on this so I will go ahead and blog on it.
You don't have to dispose of the empty 7 day candle glass jars. You can continue to work them and get "more bang for your buck". For example, I got rid of my money pot and instead use an empty 7 day "Lucky Flame/Money Drawing" candle glass and it works wonders. Once the candle has extinguished itself naturally you then simply add your ingredients to the glass jar, pray over it, mark it with oil and then you are good to go. In mine I like to only add silver coins to the jar, such as nickels, dimes, quarters, etc. My jar's already full so I'm going to go cash the money in for the largest bill possible and then place this back into the bottom of the jar. I will then continue to add silver coins to the jar until it's full once more. I will just keep repeating this over and over.
Another good way to reuse an empty glass jar is for sweetening work. Let's say you are burning a 7 day candle for peace in your home. After the candle has burnt out you will then add your pictures or names to the jar, pour just enough syrup to cover them, mark the jar with your oil, and then set it someplace where it won't be discovered. However, this trick may attract bugs so be careful.
A third way I work empty 7 day candles is what I call "water work". Basically you will take your empty 7 day glass candle, place your petition paper for whatever it is you want, place perhaps a pinch of whatever condition powder or herb you want, pray into the empty glass so that you fill it with your prayers and can see your breath on the inside of the glass, and then fill with fresh water. Mark the jar with oil and then set it aside. As that water evaporates your prayers will be carried forth.
I think most people also know that after you burn a 7 day novena to a saint you can then use the empty glass jar as a vase for putting flowers in as an offering to that saint.
Finally, I will share what "marking with oil" means as I'm sure some people don't know what I mean by that. When you fix your empty 7 day candle glass you will do your thing and then you will take whatever oil you are using. You will trace your finger around the rim of the glass in a clockwise circle to draw whatever it is to you. Then you will make three crosses on the glass with the oil while saying, "In the name of God the Father, God the Son, and God the Holy Spirit, Amen". Then you are good to go.
I will give a ward of warning though. I personally do not work with empty glass jars where the candle burning omens were not good. I would recommend not using those glass jars in this fashion.