Water-washable resins
Water-washable resins
A recent development in 3D resin printing is the appearance of water-washable resins. These, as the name suggests, can be washed off and cleaned in simple tapwater rather than alcohol (some people might prefer to use distilled water if their tapwater is particularly “hard” or chemical-treated).
Things that stay the same
The big thing that everybody stresses about using water-washable resin is that it doesn't simply means that you can clean your prints in the sink, under a running tap, and let all the waste go down the plughole. The resin itself is still toxic, and the water with resin dissolved in it still counts as hazardous waste. If you have this stuff lying around on pools on your bathrom sink, and the water evaporates off, then what’s left is a film of pure toxic uncured resin. Yuck.
All water that’s used to wash prints needs to be kept and stored, just as if it was resin-contaminated alcohol, for reuse. Like alcohol, if it’s become too dirty for re-use, you can leave it out in direct sunlight for the water to evaporate and the remaining resin to cure and become harmless.
Things that are better with water
While water-washable resin doesn't completely eliminate washing hassles, it does at least mean that you are dealing with one less hazardous material. You can pour contaminated water into a shallow tray in direct sunlight and let it evaporate without worrying about filling your house or flat with potentially explosive fumes, spilt water isn't a fire risk, and you no longer need to worry about storing bottles of highly flammable material.
Pure and nearly-pure alcohol also kills living tissue on contact, and while living skin has a protective surface of dead keratinised cells, any pure alcohol that gets into your pores can cause subsurface tissue damage. While we recommend using barrier cream in addition to gloves, barrier cream is a far more effective barrier to water-borne nasties than to those dissolved in pure alcohol, as alcohol will dissolve the fats and oils in the cream (and also any proptective fats or oils secreted by your body).
Dealing with pure-ish alcohol is a hazard and a health hazard in its own right, even without resin being involved.
The above deals with the "best-case scenario" of using pure ethanol (the type of alcohol that appears, diluted down to a few percent, in alcoholic drinks). If you’re using methylated spirits or “denatured” alcohol to wash your prints, then, in order to avoid having to pay the taxes due on “drinking” alcohol, the manufacturers deliberately add poison. The alcohol is usually denatured (= “contaminated”) by adding a quantity of poisonous //methyl// alcohol. Methyl alcohol does terrible things to the body, including nerve damage, and it’s why meth drinker typically go blind and insane. So methyl alcohol is nasty … and it evaporates like ethly alcohol, and you breathe it in, and it is absorbed through the skin on contact.
Things that are more complicated
At first sight, it might seem as if there are no disadvantages at all to using water-washable resin rather than a conventional alcohol-washable formulation. There may be an effective price premium of a pound or two on a bottle of "water-washable", but since you no longer have to buy expensive solvents, the price-differential pretty much disappears, and you no longer have to worry about storing flammable solvents on-site. Given that the detail on the "w-w" prints that we tried were at least as good as with a comparatively-priced standard resin, one might wonder why water-washable hasn’t already become everyone's default choice.
The main reason that standard resins still seem to dominate appears to be their diversity – there’s no shortage of companies making and selling standard UV resins, they are available in a reasonable range of colours, both clear and opaque, if you have a number of colours in the same formulation you can try mixing intermediate colours, the Monocure CMYK kit lets you produce almost any other colour you can think of, and when you buy your first 3D printer, if it comes with a starter bottle of resin, that resin will probably be alcohol-washable by default.
It is also possible, at a price premium, to buy “special” resins that are extra-hard, extra-tough, or extra-flexible (rubber-like).
If your prints are all going to be painted, or you don’t care about colour, then perhaps it’s worth making the switch and completely eliminating alcohol-washables from your workflow (and making a note of alternative suppliers, in case one is out of stock). However, if you need a wider range of colour options, or custom colours, you may then need to keep stocks of both types of resin, along with washing alcohol and all the alcohol-related infrastructure, which means ending up with two different sets of incompatible resins that can’t be mixed, and probably some duplication of washing and storage containers.
Even so, it still might be worth using water-washable for print runs that will be painted, or that have the right colour available in water-washable, or for prototyping, when the convenience of not having to use alcohol for //those// prints may outweigh the inconvenience of switching between different resin types.
