What is gesso?
Gesso (pronounced ‘jesso’) is basically a paint mixture used to prepare a surface for painting – often for oil or acrylics. It usually comprises of a binder mixed with chalk or gypsum and sometimes it has a pigment added to it too (usually Titanium White). Water- and oil-based gesso mixtures are available but generally speaking an acrylic (water-based) gesso will be suitable for both oil and acrylic paintings. Understanding the difference between gesso and primer can be confusing as many use the words interchangeably. Basically: gesso is a primer, but not all primers are gesso. Modern primers – including canvas primer, board primer etc contain a range of ingredients to suit various needs, whereas the basic ingredients of gesso are binder, chalk/gypsum and pigment. Traditional gesso was made using animal glue (usually rabbit-skin glue) which some still use today.
What does one use it for?
Gesso is used to prime a surface (wood, paper, canvas etc) to prevent the paint from soaking into the surface too much and also gives the surface a bit more texture or “tooth” which will help the paint to adhere better. It can also be useful in stiffening the surface especially when used on fabric or paper.
How do I apply gesso?
It is quite simple and straightforward to apply gesso to your surface. All you need is a suitably-sized brush and your gesso! Go ahead and paint it straight on making sure to cover your surface evenly. If your gesso is water-based you can thin it down with a bit of water – this will help to make a smoother surface. The number of coats needed depends on your personal preference – two coats usually works well. If you’d like to tint the gesso you can add some acrylic paint in the colour of your choice.
Do I need to prime my store-bought canvas?
Usually store-bought, pre-stretched canvasses are already primed (i.e. have a coat or two of gesso) but if you find the canvas too smooth or you’d just like to add an extra coat then go ahead – but generally speaking, its not necessary. It should be quite easy to tell if your canvas has already been primed by comparing the front and back of the canvas – often the primed side will be more white and the grain of the fabric will appear to be more filled in. Always make sure to check if your canvas has been primed specifically for oil painting or if it can be used for both acrylic and oil painting.