So, for work I use 91% ISO to clean resin prints. Any excess resin on the models mixes with the alcohol and thus the alcohol will progressively exhibit: A) cloudiness B) a green tinge. I use transparent green resin so this makes sense. I call this stage 1. I transfer used alcohol into recycled glass canning jars. Anywho, the resin cures with UV light, sinks to the bottom and forms a sludge layer, and the green color fades to a yellow. this is not a perfect process, which has caused some frustration on my end. When the alcohol reaches this point I call it stage 2. I've recently been researching how to properly clean and filter my alcohol so as to recycle it as much as possible. One document I read suggested leaving used alcohol outside in the sun for several days. I have a porch that gets a fair amount of sun during the day. So, I've decided to run a few experiments and keep track of progress. Starting with leaving 3 bottles out in the sun for several days in a row. Once as clear as possible, I am going to strain them through a couple micron filters and then repeat the process. I put these 3 bottles out Wednesday morning. Leftmost was yellow green, right two were pretty much emerald green. Unfortunately I did not think to snap a photo at the time. This is how they looked after the sun went down.