When the issue of plastics in the oceans came to the fore a few years ago I started worrying about what to do with the wash water after using acrylics. I researched manufacturers’ websites, even emailed a couple, and was a bit surprised that this issue wasn’t highlighted. The only exception I found was Golden who have a page on their website describing how to filter the solids out of the water. Not only that but it included my favourite word – flocculation!
The process involves using Aluminium Sulfate to cause flocculation of the paint particles. Hydrated Lime is then used to neutralise the mixture. Both chemicals are available in powder form.
I found the instructions in Removing Water-Based Paint Solids from Rinse Water simple to follow, but there were a couple of things I eventually discovered out that make things easier.
What coffee filters to use?
The filtering process is quite slow so it is worth having large filters that you can fill with plenty of waste water and leave. The instructions give some filter suppliers but are written for a US audience.
I started with the biggest coffee filters I could easily put my hands on – 6 cup ones. These were too small. What I needed were basket filters.
I got some Bunn brand basket filters. Laid out flat they are 35cm diameter with a 13cm base. I save my waste water in 5L bottles. With the large filters I can filter this amount in just two pours. Each pour takes about 2 hours to filter through.
How to hold the funnel above the bucket?
If you use a funnel you need a method of holding it above the bucket that collects the filtered water. Don’t use a funnel, use a collander instead. This can simply sit on the top of the bucket. It also has the additional advantage that water can come out of the edges as well as the bottom, enabling it to filter quicker.
I use the Golden instructions and can easily filter 5L of waste water in a day with just two pours. Golden have now introduced a product, Crash, which includes the chemicals in liquid form. This must be more convenient than handling them as powders, but is more expensive.