Hi, my name is Larry Keith, i'm Head of Conservation and Keeper and I'd like to
give you a little update on our work on Piazzetta's 'Sacrifice of Isaac'.
I'm here with my colleague Kendall Francis and as you can see the picture's moved on
a long way from the first video. I talked before about how the painting had had a
kind of unfortunate conservation history where it had been really quite seriously overpainted
and extensively overworked and more recently you may have seen some footage of the picture after
cleaning with all the losses filled white but no retouching begun, it looked a little bit alarming,
but I think you can see that the picture is progressing beautifully
as it's being worked on by Kendall who I'd like to have explained the work to you in more detail.
Hello my name is Kendall Francis and I'm a Conservation Fellow here at the National Gallery
and alongside Larry i have been treating this painting by Giovanni Battista Piazzetta.
So my colleague Larry cleaned the painting and the next stage of treatment was to meticulously fill
all the losses and this resulted in the painting looking a bit like a snowstorm with hundreds of
tiny white fills across the whole of the painting and to some to see all the losses could seem quite
intimidating or somewhat daunting but in actual fact much of Piazzetta's work remains in very good
condition and well preserved and although it is an immense project it is very much an achievable one.
During the retouching process we use a modern stable conservation material and along with a
diluent we retouch the losses to match the surrounding areas. Even after applying this
golden ochre colour to the fills it's already slightly knocked back the striking white colour
of the fills and already it's enabled a much better reading. The reason why we chose this
golden ochre colour as the kind of ground base colour for the fills is because in the original
painting the original ground is mostly made up of yellow earth pigments so this enables us to
work up from a similar base colour during the retouching phase which we are now currently on.
So in opposition to Roger Fry's quite extensive, large-scale retouchings that covered a lot of
original paint we are taking a much more precise and controlled approach to the retouching and this
method allows us to actually in contrast regain Piazzetta's quite loose and fluid brushstrokes
and also how he has confidently applied the second composition of Abraham and Isaac on top
of the original sketch underneath and this is explained in the previous video linked above.
The most challenging aspect of the retouching has been trying to distinguish the dialogue
between the two sketches and it won't be until every single loss has been
reintegrated and retouched will we actually see Piazzetta's mind
working on the canvas and actually letting the compositions speak for themselves.
Piazzetta's palette is typically Venetian, you can see here in Abraham's red drapery that he
has used a colour called 'venetian red' which is commonly known as red ochre and
he has used mainly ochre and dark earth pigments and this commonly sets him apart from his
more vibrant and bright counterparts like Tiepolo and a good example of this is the 'Allegory with
Venus and Time' which is actually in the National Gallery collection. However i feel Piazzetta has
still maintained this sort of luminosity through the use of a lighter coloured ground and perhaps
due to the inclusion of a pigment called realgar. Realgar is a bright orange pigment
and this was typically locally used in Venice and Piazzetta has incorporated this in his
darker passages to maintain this luminosity and give the painting a much more golden hue. Now this
painting has been challenging due to the two sketches and the fact that
across the whole of the painting each tiny little loss can be a complete different colour
due to the fact that you can see here this is where the original head of the below sketch
is and piazzetta would have used darker earth pigments whereas here this part is straight
on to the ground colour so the two localised areas can require two quite different colours.
So the retouching has been absolutely fascinating and rewarding and it's been brilliant to see
Piazzetta's loose brushwork slowly evolve. You can see here I have started to retouch so this
area was the same with all these small losses and you can see that i've started to regain some of um
Piazzetta's brush strokes and how he has applied the above composition on and I've also worked on
the face of Abraham which is quite a repetitive face we see in quite a lot of Piazzettas work.
The next stage will be after all the losses have been reintegrated and retouched will be a final
varnish and the very much now displayable picture will be able to be seen on the gallery walls.