There is a product known by several names like water marbles, crystal mud and such. These are tiny polymer beads (smaller than a BB) that when soaked in water grow around 10x there size as they soak in the water, over time, the water will evaporate and they will shrink again but it takes weeks or even a month.
I saw that some people were using these with water that also had a fragrance mixed in (water soluble fragrance) and they used them as air fresheners. So I decided to do this and I made this lid system that the openings can be varied for different amounts of fragrance.
Please read the Instructions page for specifics.
I prefer printing these in ABS but you can print them in whatever you like, if not ABS though you will need to glue the parts together.
Print out at any resolution you desire. Print at least 2 of the pins at a time to prevent distortion from heat since they are tiny and the tallest object.
Once printed, insert the pin into the largest piece (top) and then into the next one (top spin) and then put a drop of acetone (for ABS only) onto the bottom of the knob and shake away any excess, then place the knob onto the pin and press down until it's got good contact with the top plate. Twist the top and bottom plates to assure they move, there should be a little friction.
Set it aside and wait for the ABS to evaporate and it's ready to use.
The crystal marbles need to soak in a mixture of fragrance and water (depending on how strong your fragrance is, it may be a 50:1 mix) for 12 or more hours, then drain off the excess liquid and place the marbles in the jar with the new lid in place and open to the desired amount.