Rollo Q asks: “I’ve a few questions in regards to the casein. Roughly how lengthy do you discover the paint is moist (moveable somewhat than liftable) on the floor. Clearly I realise this should rely upon local weather and floor and paint thickness and so forth, however I’ve seen individuals name it quick drying and its arduous to inform what which means (I paint in flashe vinyl which is notably slower than acrylics however quicker by far than oils. Open time is 30 – 60 minutes for flashe I would guess). Additionally do you utilize an acrylic varnish? Or a resin?”

James Gurney solutions: You are proper, time it takes for a freshly painted space to dry to the contact is determined by the temperature, humidity, wind, paint thickness and wetness, absorbency of the bottom, and even the kind of pigment. Cadmiums are slower drying than umbers, for instance, and titanium white dries comparatively quick. This pigment variable is particularly noticeable on the paint blobs squeezed out on the palette. 

So how lengthy does it take for a passage to dry? On a pleasant day a mean paint stroke begins to arrange in wherever from a couple of minutes to 10 minutes or so. Whereas it is nonetheless moist you may mix all you need, however as soon as it is dry to the contact, a stroke can go down over it with out a lot worry of earlier layers lifting or reactivating, until the brand new stroke is actually moist or there’s a whole lot of scrubbing. 

Paint that’s newly dry presents a comparatively closed floor, which means that, not like gouache, it resists reactivation. The energy of the paint’s glue-like binder is just not as robust as acrylic, which has a robust bond which sticks arduous to your palette and wreaks havoc in your brushes. Due to that weaker binder, casein methods involving thick, textural impasto ought to solely be painted on a inflexible floor reminiscent of a panel or illustration board. 

With casein, paint that feels dry from evaporation is not absolutely cured but. The milk protein molecules preserve bonding, which might take wherever from in a single day to a few weeks. Curing time could be accelerated by placing the portray in a sunny, dry, and heat (however not too scorching) location. 

After it is dried and cured you may resolve whether or not or not you wish to varnish it. Like gouache, casein is supposed to dry matte, and that may look good in a light-weight, high-key portray. I virtually by no means varnish sketchbook work. Work with a matte floor actually {photograph} nicely, and the digital model of a portray could be adjusted in Photoshop to present it the total vary of values. The producers counsel buffing the floor of a dry portray utilizing an previous T-shirt so as to add some semi-gloss luster to the floor.

The primary cause I varnish a few of my casein work is to deepen the darks in an total darkish portray or to guard a portray that I wish to body with out glass. Darkish-keyed work look higher varnished, and typically varnish is required to unify the floor sheen of the portray. You may varnish casein simply as you’ll varnish an oil portray. The benefit of casein in contrast with oil for plein-air painters is that you may varnish it the identical day, somewhat than ready weeks or months for the paint to dry. 

For the varnish to work with one or two coats, the substrate beneath the paint must be comparatively non absorbent, reminiscent of a hardwood panel or gesso-primed canvas mounted to board. I have been portray on acrylic primed canvas panels, which reply nicely to varnish. If the portray consists of skinny casein washes on gentle watercolor paper, the floor will take up the varnish, and it’ll take a whole lot of coats earlier than you begin to get a shiny floor. After it is varnished, a casein portray could be framed with out glass identical to an oil.