Hi, my name is David Peggie, and I'm a chemist in the Scientific Department of
the National Gallery this video is part of the 'Chemistry of
Colour' series where we focus on one pigment in a painting.
Today it's a bit different though, as I'm speaking to you from my living room.
Titian painted 'Diana and Callisto' in Venice in 1559
for King Philip II of Spain. Today we're going to look at Titian's use of red
lakes. You can see this in areas such as the
pink drapery of the nymph. Red lakes, when mixed with an oil binder,
produce a highly translucent paint. When layers of translucent paint are
built up over an opaque under layer, these layers, often described as glazes,
produce rich deep colours. Artists like Titian used
this technique to paint draperies, giving them a lively surface
that very effectively evoke the crumpled texture of the fabrics.
Unfortunately, red lakes often fade over time with exposure to sunlight,
so the textiles we now see in the paintings have lost some of their
initial splendor. Lake pigments are made from organic dyes
obtained from plants or animals. In this example, we're using
Mexican or 'New World' cochineal insects. They contain a large amount of a dye
molecule known as carminic acid. Much more than their Armenian or Polish
old world counterparts. In fact up to 20% of their mass is
dye, and they're easy to harvest because they
live as parasites on cacti. In fact because they are such a rich source of
colourant and easy to acquire, they're still used as a source
of dye to this day. If you have red food colouring, look out
for E120 on the label - that's cochineal. There are many variables
that can affect the precise hue of a lake pigment,
but one of them is the source that was used.
The one that we're doing today is from Mexican cochineal, this is the
Mexican cochineal beetle. I've also got some examples of the
pigments. They can be slightly different colours,
so this is a pigment made from cochineal, this is a
pigment made from brazilwood, and the madder root's are very
reddish, brick red. Red lakes are not
straightforward to make. Step one, we have to extract the dye from
the source. In this case we've ground up the cotton
and are boiling it in an alkaline water. Step two, the dye is soluble, but we need
something insoluble so we can use it in a paint.
So to make a pigment, we have to add alum. In addition to the alkaline water,
hydrated alumina is formed, which then precipitates out of solution,
bringing the dye molecule with it. We only want to add alum as it's
precipitating. Once it stops fizzing that means we've added
enough, and we're not going to get any more pigment. You're watching the pigment
forming. Step three, coloured precipitate is then
washed, so we're left with just the pigment.
The pigment can then be mixed with a binder to produce a beautiful red
translucent paint. In the paintings Titian completed
before the 1540s, the red lakes were generally made from
madder root or a scaled insect called kermes, but after the 1540s
he switches to using lakes made from cochineal.
Why? Well, because of the discovery and establishment of trade from the Americas.
Mexican 'New World' cochineal first arrived in Spain in 1523,
and by the 1540s was being used by Italian dyers,
because each insect contained such a large amount of dye. This 'New World' cochineal
was extremely economical. Its use was officially sanctioned by the
guilds in Venice in 1550, so much of the red lake pigment
available to Titian will have been made using this 'New World'
cochineal, and it's probably for this reason that
it's been identified as one of the red lake sources used in Titian's 'Diana and
Callisto'.
If you're interested in learning more about the Gallery's collection, click
here or here. Thank you for watching, and we'll see you next time.