Conserving Vulture Peak | Ep4: Liquid Chromatography Mass Spectrometry


So today we’re going to get Diego and
Joanne from Science to come up and have a look at the dyes in the embroidery
because it’d be really useful to find out what kind of dye stuffs were used to
colour the embroidery threads. Also it might help us understand if the colours
have changed, because we do think there are quite a few areas where we’ve had a lot
of fading going on. And by doing some dye analysis we might actually find that
maybe some of the beigey browns were actually maybe pinky red colours. The method which they’re going to use to identify the dyes is a destructive technique and does involve taking small samples – It needs about half a centimetre length of each fibre. And so because it is destructive we have
thought very carefully about whether this is appropriate and I’ve discussed it
with the curator, but on balance I think that what we will learn about the embroidery
outweighs the sacrifice of a small sample. Hello everybody. My name is
Diego Tamburini and I’m a postdoctoral research fellow at the Scientific
Research Department of the British Museum. My main task is to analyse
organic colorants in archaeological textiles. Today all the dyes that we have
on our clothes or that are used to dye textiles are synthetic. Whereas in
antiquity people were using natural substances to create colorants to dye
their clothes and create artistic objects. This is just a small part of the
British Museum reference collection. Every time we look at something that
comes from a specific geographical area we need to have the proper reference
collection and this is how the collection of the British Museum was
built. We worked on different objects from different geographical areas from
all over the world and during the years people actually went there and acquired
reference materials, to be able to compare their results to
this. Today I’m going to work on some samples
taken from a famous Chinese textile, referred to as the Vulture Peak. I was
with Monique and Hannah and we were sampling the textiles and what we did
was take a small amount of fibres and we put them between two glass
slides and labelled them. We did this because we wanted to be able to look at the fibres under
the microscope with high magnification in order to understand if the threads
were dyed one by one or if they were dyed altogether.
If mixtures of colorant were used. So the microscopic observation already gives
important information about the dyeing technology. The next step is when we
separate some of these fibres, we put them in these vials and we perform the
extraction of the dyes from the fibres. What I’m about to do is to add 200
microlitres of this mixture of solvents. And we are adding a little bit of oxalic
acid which is the agent that allows us to break the bond between the dye
molecules and the fibres. OK so what I just did was to put the
samples in that heating block. They are going to stay there at 80 degrees for 15
minutes because the heating is going to help the extraction reaction. OK so after 15 minutes we have to remove them, and the next step is to dry them under
nitrogen because I want to get rid of the acid, I want to
get rid of the acetone. I don’t want them to be in my final solution. So now I turn the nitrogen on. And it is going to take let’s say one hour before
all the solvents evaporate. OK so now we are at the end of the extraction
procedure. Our samples are ready. Our dye molecules are dispersed in this solution
and the solution is OK to be analysed using high-pressure liquid
chromatography mass spectrometry The dye molecules are separated inside
the machine and the result is a graph which is called chromatogram which shows
different peaks at different times. And each peak corresponds to a molecule.
So what I will do next will be to compare the peak I find in my
samples with the peak I have from my reference database. And by doing that I
will be able to say ok this red is made up of madder rather than cochineal, or
this yellow is made up of the extract from this plant rather than this other
plant. So these are all the information that I can get from these results. So everything you’ve seen so far is not actually the real time-consuming part.
The time-consuming part is the interpretation of the results and from
that try to reconstruct the natural origin of the dyes that were used on the
Vulture Peak. We are talking about China and 8th century. So they might have
used some very local and particular plant which I might meet in my
collection. And I’m going to be able to reconstruct the original colours of the
textile which actually shows a lot of fading so everything that now we see
orangey, yellowish might have been red for example and I can say that from this
kind of analysis. And there is a little little stripe of a purple dye. Purple
dyes are very, very delicate and precious. We are talking about a very expensive
colorant it derives from some little shells and each shell produce a little,
little bit of purple. So if that purple is there we are talking about what is
called true purple and in that case it might be a very, very nice
discovery. So let’s see.