I’m currently teaching a couple of on-line classes with the Ottawa School of Art and this week was a biggie – colour, pigments and acrylics – all subjects that generate a lot of interest.
Judy wrote: “Thank you David. I have a couple of questions….When you are painting shadows, do you use exclusively purply shadows or greeny shadows throughout the entire painting or do you use both?”
With portraits I may use one or the other and sometimes both…I’m not consistent. Oftentimes I’ll start with one and the other creeps in.
“Also is a glaze another word for medium or is it a process you use with a medium?”
Glazing is the process of applying transparent paint, using medium and pigment. In the store, for acrylics, you may well find “Glazing Medium” – medium suitable for the process of glazing.
“And if you don’t have Hansa Yellow do you get the same effect if you use a combination of Cadmium Yellow Light and Lemon Yellow?”
Cadmium Yellow Light is very close chromatically to Hansa (so you would not need Lemon) but it’s slightly more opaque and so maybe not quite as good a choice. If you matched Hansa a with Cadmium regular and Lemon, which is certainly possible, it too would be more opaque.
“Also I have a canvas on which I sketched a portrait with oils years ago. If I put the acrylic wash over it and then wipe out the highlights will the acrylic cover the oil outline?”
Unfortunately you can’t paint acrylic over oil…the rule is: only oil over acrylic. Sticky acrylic gesso might well adhere to old oil for a time however not forever. The reason is, oil paint actually oxidizes rather than dries and hence is never fully “dry”. That’s why cracks may well appear over the centuries. Placing a layer of what is essentially plastic over the top sets up an unstable paint sandwich.
“I’ve done only one acrylic painting in a workshop which I didn’t finish as I’m not used to them and I work very slowly and acrylic dries so much faster than oil. Will the medium slow the drying?”
Medium does have the effect of slowing drying time, not because it dries slower but because physically there’s more stuff on the canvas to dry. You can add a retarder to the paint/medium mix (follow the instructions) or buy a slow-drying set of paints such as the Golden “OPEN” series. They dry a lot more slowly than regular acrylics.
Barbara also asked: “Certainly I know that watercolour paints are transparent or opaque, but confess to have learned from you this past Thursday that acrylic paints are also transparent or opaque. I thought that they were all opaque. I looked at my collection of acrylic paints and found only one tube which had an indication of transparency or opacity. Am I missing something? Is there a symbol to look for on a tube of acrylic paint?”
Major manufacturers normally include a transparency rating, sometimes in the form of a symbol such as a square, filled or not to denote the degree of transparency. Because there is no standard, if in doubt I’d check the manufacturers website.
“In general, if a watercolour pigment is rated as transparent, would the same rating be true of the equivalent acrylic pigment? For instance, cerulean blue appears to be opaque in both watercolour and acrylic paints.”
Yes indeed – it’s essentially the same pigment, immersed in a different medium: watercolour in gum arabic or similar, acrylics in acrylic polymer (and in oil painting for that matter the same pigment is in oil).
Hope this helps!
David