What is acrylic retarder?
As the name suggests, this slow-drying medium slows the drying time of acrylic paint. Only a tiny amount is needed, up to 5%. It does not change the colour or finish of the paint. The length of the extended drying time will be influenced by prevailing temperature and humidity.
How much acrylic retarder should you use?
Adding over 8% MM1 Drying Retarder will compromise the water-fastness of the dried paint by slowing the cross-linking of the acrylic. Therefore, although the paint may appear dry, it can be re-wet with a wet brush or cloth.
Using acrylic retarder on raw canvas
On raw canvas, adding 3-5% MM1 Drying Retarder, pre-diluted with water, will improve the mixing of inorganic pigments, oxides, earth colours, titanium dioxide and metallic pigments.
What happens if you add too much drying Retarder?
Drying Retarder will slow the evaporation of water from the paint. However, excess amounts of MM1 Drying Retarder (over 10%) will severely restrict the "cross-linking" of the acrylic. Therefore, even though the paint may look dry (and indeed, all the water will have gone from the colour), it will not have "cross-linked" or "cured", so it can be re-wet, i.e. with a wet brush or cloth. This allows the Matisse acrylic colours to be used just like watercolours. Available in 250ml bottles
How does the paint dry?
So one of the first things to think about is how paint dries okay, probably like watching grass grow, but it is pretty interesting on an atomic or microscopic level. What happens if you think of many balls filled with water in a big room? Now imagine the water evaporating off the top. All the little balls and the little beads are starting to push together. Still, the top is cross-linking, or in simple terms, it's joining. These beads join together, which we call coalesce or curing, to form a plastic strip. This is basically what acrylic is what the paint is, and it creates this strip of plastic and all the little beads chemically bond together to one thing impregnated with the pigment of the colours.
Acrylic retarder in the paint-drying process
That's the basis for the paint. What happens with the drying retarder is it wraps itself around those little beads and doesn't allow them to join together. It slows them down, slows the drying time of the water or the evaporation of the water. So this is why if you put too much retarder, it can stop these little beads from joining together.
What it does is it will stop them from curing, so as we said, the paint dries from the top of the beads, in turn, the beads join together as they cure and what is trapped underneath then the colour is not dry. You'll see this a lot on your palette when you are painting where the thick paint forms the skin, which is the top drying and starting to cure but the water is trapped.
Now with the drying retarder, we're trying to stop those beads at the top from joining and curing, which will do that to a certain extent. There will still be curing, and it will still form a skin. It just takes much longer to do that. the retarder will slow the evaporation of the water, and it stops the "little balls" from joining together
Paint drying with too much acrylic retarder?
Now, if you put too much drying retarder in, What will happen is those little beads of acrylic are not going to be able to touch each other to join together chemically, so for all intents and purposes, the paint could be dry if it looks dry. Still, it hasn't been cured. There hasn't been that linking going on.
So what you've got is a lot of little dried bits of acrylic that they haven't bonded together to make that nice film coating which is what we're after, so we've got a dry film, and it looks as though it's dry and it's cured. But if you take a wet rag, it will come straight off because there's been no bonding. It hasn't stuck together. It hasn't adhered; it hasn't glued. So it's going to come straight off. It might take several months for that drying retarder to evaporate out eventually.
Safety Data Sheet for Matisse Drying Retarder (SDS)
To view or download a copy of MM1 SDS, please CLICK HERE (271kb)
