Narrator: Summertime Number 9A is one of Jackson Pollock's famous 'action paintings' - in which he poured and flicked paint onto a large canvas on the floor. But what kind of paint? Stand anywhere along the length of this picture and take a closer look - and you'll see very different materials. Conservation scientist Tom Learner:
TL: "The black and the silver-grey paints, we know from analysis, are a form of house-paint. They would have been extremely fluid, poured onto the canvas, probably with sticks or the handles of brushes. And compare that to the artists' oil paint - the bright yellows, the two blues, the reds, the greens, the ochres. Probably taken straight from the tube and applied in a traditional manner with a paintbrush.
The house-paints being used by Pollock here are all oil-based - very similar in fact to the sorts of paints being used to paint a door-frame. There would have been a lot of organic solvent - probably turpentine - from within the paint itself and perhaps also Pollock would have also diluted the paint down a bit further - so it would have been an extremely smelly process!
In many areas, particularly the black and grey paints, you can see wrinkling in the surface. This is a common phenomenon in house-paints, when they are applied a little bit too thickly, a skin can form on the surface and as the underlying parts dry so wrinkling forms. You can also see quite clearly differences in the physical properties - in other words how brittle the paints are. You can see distinct cracks, vertical and horizontal, in the black and grey areas whereas the artists' oil paint is still pretty flexible and no cracks are apparent there.
The background of this painting you can see is the canvas - there is no pigmented priming or ground layer on top of it. Although we have detected a transparent coating, an animal glue, very very thin. If you look closely at some of the poured areas perhaps in the black paint you'll see that there are some extremely narrow bands of colour and without that animal-glue size those thin lines would probably have bleeded out to a much wider appearance.
Another big difference between the times of paint would be in the drying time. The first part of the painting would have been the canvas laid flat on the ground. The house-paint was then poured and dripped and then Pollock after maybe a day or two, once that house-paint had dried, reasonably quickly, would have come back with these far more calculated, carefully placed areas of bright artists' colour.
So although this painting appears extremely spontaneous I think the evidence from the different kinds of paint being used shows there was in fact a huge amount of planning that went into it."