If you use high concentration alcohol in the alcohol bath for your resin printer, you know that it can literally vanish into thin air if you don’t store it properly. It needs to be kept in an airtight container or else it will slowly evaporate and become a waste of money. Another issue that can arise is if too much resin or debris builds up in the alcohol bath, and then affects the quality of your prints. I had a print once where after I rinsed it in the alcohol and cured it, I found that some resin debris from the bath had stuck to it, which obscured some of the detail on the piece.
So how can you clean and recycle the alcohol in your alcohol bath so that you don’t waste it or ruin your prints? You can expose the alcohol bath to ultraviolet light, which will cure the dissolved resin within the bath, and then filter out the solid debris. This will completely remove the resin from the alcohol and leave you with a crystal clear alcohol bath once again. I’ll explain how I do that and what else is involved.
Types of Containers
The type of container you use to store your alcohol is important. It needs to have a tight seal on the lid to prevent the alcohol from evaporating. It also helps for it to be clear. Having a clear container for your alcohol bath will allow you to expose it to UV light without opening the container, which would let the alcohol evaporate. It doesn’t matter if you use a double bath or a single bath, because they will both accumulate resin and debris and need to be cleaned out eventually.
The container I use is a 1.8 liter clear food container with a rubber lid that has a twisting lock on top. This makes it easy to open with one hand if I’m holding the 3D printed piece in my other hand getting ready to rinse it off. I like to open the lid at the last minute and then close it right after I put the piece inside to minimize the amount of time that the alcohol has to evaporate.
Ultraviolet Light Exposure
There are a few different ways you can expose the alcohol to UV light to cure the resin in the bath. The best way, in my opinion, is to place the alcohol bath on a windowsill where the natural ultraviolet radiation from the sun will slowly cure the resin. After a few hours there should be a layer of solidified particles on the bottom of the container, as long as it was sitting still the whole time. Depending on how much resin was dissolved in the alcohol, the amount of time it takes for it all to be cured will vary. It could take a whole day or more, or just a few hours.
Direct Sunlight
One thing that I’ve thought about but not actually tested is what would happen if you put the alcohol bath outside in direct sunlight, as opposed to on a windowsill indoors exposed to diffused natural light. Because the container is clear, it would probably produce a greenhouse effect and rapidly heat up the air inside the container. I’m not sure if the build up of heat and pressure would be enough to cause the airtight container to explode, but seeing as it is full of a highly flammable liquid I wouldn’t take the risk.
Another method of curing the resin in the bath would be to use artificial UV light. If you use an artificial UV light source to cure your prints, like a nail polish curing lamp or other device, you could simply use that. If your curing station is big enough, you can put the whole alcohol bath container inside of it, but if it’s small like some nail polish curing lamps you can simply sit the bath in front of it. As long as the alcohol is being exposed to some UV light it should suffice. The disadvantage of using this method is that it uses electricity to power the UV light bulbs, as opposed to sunlight which is free.
I tested this method by putting my alcohol bath container in front of my nail polish curing lamp and I noticed a few problems. Instead of slowly curing the resin and having it sink to the bottom like the sunlight method, the UV lamp cured it very quickly and mostly on the side that was directly in front of the light. It built up a thick film on the side of the container that was difficult to clean off, and that film sort of blocked the light from getting to the rest of the alcohol.
Another problem is that my curing lamp can only stay on for a maximum of thirty minutes, so I had to keep turning it back on for a few hours until all the resin in the bath had cured. I would much rather just leave it on the windowsill and come back to it later when it’s done.
Filtering
Once all the resin is cured and you’ve let it sit still for a long time, there should be a layer on the bottom of the bath of all the cured resin. Hopefully the alcohol on top is crystal clear and like new. Now all you have to do is filter out all of the solids. There are a few different things you can use to do this. I just used a paper towel folded up into a funnel shape, and that worked fairly well, but it didn’t filter out the very fine particles.
Some people have suggested coffee filters and those would probably work similarly well. From my experience, you don’t need a special filter for a the very fine particles as long as you let the alcohol bath sit for long enough that all of the solids sink to the bottom. Then you just carefully pour it, making sure that you don’t agitate it too much, and the solidified resin particles should mostly stay on the bottom. I used just a disposable cup to pour the alcohol into.
Once you are left with the solids you can remove them from the container and throw them away. Certain containers, like mine, have an issue with the particles sticking to the sides. All I can say is that it helps if you don’t let the resin just sit there and dry, because it becomes very hard to remove it after that. Make sure to wipe it all off while it’s still wet. Then once the container is clean you can pour the alcohol back in. That’s all there is to it.
Remember that every time you open the container and pour out the alcohol you’re letting it evaporate, so try to get it done in one pour. That means exposing the alcohol bath to UV light long enough to cure all the resin inside of it, and letting it sit long enough for all the solids to collect at the bottom. Then the alcohol on the top should be pretty clear even before you filter it. The filter only stops the large clumps from getting into the clean alcohol.
Important Safety Tips
It’s a good idea to wear gloves when you do this as resin is toxic and should not come into contact with your skin. Also it’s best to work in a well ventilated environment so that you don’t inhale too much alcohol and resin fumes. There is also a risk of fire when dealing with alcohol in general, but especially high concentration alcohol. Make sure that you are not near any open flames or anything that produces sparks, even some electronics.
Related Questions
What concentration of alcohol should I use for the alcohol bath to a resin 3D printer?
Most resin manufacturers recommend that you use isopropyl alcohol with a concentration of at least 90%. Many stores will carry 91% isopropyl alcohol, and 99% concentrations can be purchased online.
How long should I wash my resin 3D prints in the alcohol bath?
Some people recommend that you wash the part or let it soak for around 10 minutes in order to fully dissolve all of the resin left on the piece, but in my experience most of the excess resin is removed after just about 30 seconds of swishing the print around in the alcohol.