Have you ever stood amongst the jostling crowds in front of the Mona Lisa at the Louvre, craning your neck to get a glimpse through the forest of phone-wielding arms?

One thing is certain – she certainly draws a crowd. I wonder if the mystery sitter could have imagined in her wildest dreams the stir she would create as she sat for Leonardo da Vinci to have her portrait painted over 500 years ago. Many factors have probably contributed to her enduring appeal – not least the unknown identity of the sitter which has drawn endless speculation over the centuries. Add to this the 1911 heist and theft of the painting which caused a sensation at the time, and her celebrity status was sealed.

But the inherent attraction will always lie in her enigmatic gaze, and especially that barely-there smile which seems to flicker and change the longer we look at it. Much has been written about this mysterious smile and the visual tricks that the shadows seem to play, but how did Leonardo achieve this effect? The answer most probably lies in his masterful use of glazing.

A glaze is simply a very thin layer of transparent paint applied over a dried base layer of opaque paint. The glaze allows the light to pass through and gives a feeling of luminosity and depth.

The technique was developed by the Flemish painters of the 15th century such as Van Eyck. It is thought that they initially used it to create colours which were either impossible to find or prohibitively expensive. A blue glaze, for example, could be applied over a dried layer of red to give a rich glowing purple. The paints could have been simply mixed together, which would have been perfectly adequate, but those artists realised that glazing one on top of the other gave a brighter, almost jewel-like effect.

The Italian renaissance artists like Leonardo took this technique and ran with it. They discovered that multiple layers of delicate, very subtly different glazes could give the illusion of almost imperceptible shifts of tone. Scientists studying the Mona Lisa using special x-rays have detected more than forty layers of gossamer-thin glazes. Quite a dedication when you think that each layer would have to be completely dry before applying the next. It was also concluded that they were probably applied with his fingertips as no brushstrokes were visible. This is how he created those blurry, smoke-like shadows around the eyes and mouth which creates the elusive quality of her smile.

Well, we can’t all be Leonardo, but we can all have a go at adding a glaze to our painting. Forget forty layers… let’s start with one. A single glaze can really change the feel of a painting, and can create areas of depth which are quite compelling. All you need is a tube of transparent paint, some glazing liquid (or even just water will do, but I explain in the video why water might not work so well) and a nice soft brush. Click on the link here: Layering with acrylics for beginners part 3: glazing (youtube.com) to have a look at my most recent YouTube video for a step-by-step guide and any questions just ask them in the comments.

Have a go, even Leonardo started somewhere!