The average tin of paint from the hardware store is a cocktail of chemicals with names that only a chemist could love. While some are benign, many are definitely best avoided. The toxins in common housepaints include cadmium, mercury, phenols, chlorine, sulphur, formaldehyde and other volatile organic compounds. These can all cause illness for both the painters and the people who live with the painted surfaces-ranging in severity from headaches and nausea through to cancer.
ReNew and Soft Technology have run articles on non-toxic paint alternatives, but many people are put off by the extra cost of non-toxic paints (even though the avoided health costs may make up the difference). Paint also has a high energy cost. Today's conventional paints are, by weight, among the most energy intensive building products. Many of the non-toxic alternatives available in Australia are made in Europe, which means they must be shipped here, adding to their associated greenhouse gas emissions and other pollutants.
So where to get the least costly, non-toxic, low-energy paint?
The answer lies in a trip to the milk-bar. A couple of litres of skim milk will form the base for enough paint to begin experimenting. The next stop is the hardware store for some builder's lime (also called slaked or hydrated lime) and plaster of Paris. Apart from some water and your choice of pigment, these are all the ingredients you will need.
There are several variations on what is usually referred to as `milk paint'. One involves mixing lime into a thick paste with a little water, then gradually adding milk until it reaches a paint-like consistency. I was told about this method by a friend of mine, Salvatore, who had used it while growing up in Italy in the 1930's and 40's. Both ingredients were widely available, and used with various pigments, milk paint is attractive and durable. I tried the recipe using bottled skim milk, though Salvatore recommends milk directly from the cow, with the cream skimmed from the top.
I sieved the lime before mixing it with the milk, and let it sit for several hours, though found that it was still quite lumpy. Straining the mixture through muslin makes it much smoother. I used the paint on old unpainted weatherboards, and got good coverage-once it dried it actually looked like paint!
An internet search revealed some other paint recipes. One that I tried consists of plaster of Paris as the main solid ingredient, mixed with a little lime and skim milk. Again, filtering through muslin cloth to remove lumps is a good idea. This paint was similar to the lime paint, but where the lime-only paint was powdery when dry, the plaster of Paris set a lot harder.
There are many options for colouring milk paint. For a straight white, zinc oxide or titanium dioxide are good. Calcium carbonate or chalk will make the paint more opaque. Iron oxide (rust) is easy to manufacture at home from steel wool or iron filings, and gives the paint a nice ochre colour. Many traditional paints used wild berries for colouring. Again, the muslin cloth comes in handy for removing pips. If you're concerned about being able to replicate your colours, you could compromise and buy some ready-made pigment from an art supplies shop.
Besides the obvious advantage of not having to inhale pungent vapours, cleaning up these paints with water was dead simple. I didn't have to worry too much about tipping the cleaning-up water on the garden, although too much lime can be a bad thing for soil. Lime and milk paint also comes off hands and clothes much more readily than other paint. While lime is alkaline and can cause skin to dry out and feel `burnt' after prolonged contact, it is easy to dip your hands in a bucket while you paint, or wear gloves. If you get lime in your eyes flush them with cold water immediately.
Finishing the surface
One disadvantage of milk paint is that it can be marked by water. Sealing will eliminate this problem, and will make the finish generally easier to clean in `high splash' areas like the kitchen. A range of finishes can be used, including linseed oil and Danish oil. The roughness of the surface caused by particles of lime can be smoothed with steel wool or sandpaper before applying the finish.
What the ingredients do
Why milk and lime? The first reason is that they are cheap and readily available, which is why milk and lime mixes were the most commonly used paint until the mid-1800's. Most importantly, though, they have a synergistic effect that makes great paint. Milk contains a salt called casein, which reacts with calcium in lime to form calcium caseinate, a resin that binds itself with pigments in the paint and the surface the paint is applied to. Many people complain of the great difficulty in removing the bottom layer of paint on old doors and window frames-in many cases, that's well-cured milk paint. The combination also means that once cured, milk paint will no longer be alkaline.
Commercial milk paints
While looking for more paint recipes, we stumbled across an Australian company specialising in natural paints. Porters Paints, based in Sydney, were also inspired to make paint by a recipe from the past, when founder Peter Lewis discovered some paint recipes with his Grandfather's diaries. Porters range includes a cement paint called Boncote, interior and exterior lime wash, cement render and milk paint.
|Home-made paint recipes|
|Basic lime and
Mix in one part of lime with twelve parts of skim milk (you can measure by either weight or volume). Add pigment until desired colour is achieved.
Lime, milk and plaster of Paris paint
|Add plaster of Paris and pigment
until desired colour is achieved
|file: /Techref/other/paints.htm, 7KB, , updated: 2006/11/14 18:00, local time: 2014/11/26 09:29,
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