Stereomicroscopy in conservation
Narrator: Hi Dawn. Now, this looks remarkably like something I would recognise from school, a microscope from school, though that was a few years ago now. Is it the same thing, or is it a lot more high powered here?
Conservator: It’s probably about the same as one you would have used, it’s quite simple to use, but really effective.
Narrator: And what sort of things would you use this microscope for?
Conservator: For analysing surfaces, to make sure that cracks are not deteriorating or not flaking off or that sort of thing. It’s really innovative so that’s really useful.
Narrator: Can I have a peek?
Conservator: Yes, of course you can.
Narrator: Gosh, this does take me back and its amazing, you can see so much detail. Would you use this quite often then?
Conservator: Yes, when you’re doing surface analysis, this can take you up to 200 times closer and it can also go up to 1000 times closer, but the quality of the images starts to deteriorate then.
Narrator: And I suppose it’s quite quick and easy to use?
Conservator: Very easy and very quick to use and you can normally see what you want to.
Transmitted and reflected light microscopy in conservation
Narrator: Hi Laura. You’re working with one of the high powered microscopes. What does it do and how on earth does it do it?
Conservator: This optical microscope here, uses light in two ways. We can use transmitted light when we shine it through a very thin sample to look at it’s optical properties. Or, we can shine it on the surface and it illuminates the surface and it illuminates the surface and it can tell us the characteristics of the surface.
Narrator: So, you have obviously been having a look at something, what on Earth is this?
Conservator: Well this is a cotton fibre. What’s happening is the light is shining through it and we can tell different characteristics about the sample. In this case, this specific twist in the fibre indicates that we have a cotton fibre this isn’t found in anything else.
Narrator: So, it’s actually the way it looks here, not the way they go together, it’s the individual strands?
Conservator: Yes, they’re the individual structures.
Narrator: What else do you use this machine for?
Conservator: Well another thing we can do with this machine is to look at ajerite (?), which is a paint pigment.
Narrator: Now those to me just look like little bits of blue dust.
Conservator: That’s basically what they are. They are flakes of pigment, and that’s what we are looking at here.
Narrator: And this is where you use that to pass light through something. What does that tell you?
Conservator: Well the shape and the colour of the pigment and also the way that they interact with light, can help us to date the object.
Narrator: So, you’ve got that, and you can pass light through. You can also bounce light off something, how would that help with something like bits of paint?
Conservator: Well, we can also look at the cross section of the paint and what we have here is you can see all the different layers of the paint that we have going on and hopefully we can see if there is an original layer and if other bits and have been added on.
Narrator: So this is basically just a chip of paint that’s been chopped down the middle and we’re basically just looking at it side on?
Conservator: Yes, that’s all that’s going on there.
Preparing a paint cross-section for analysis
Narrator: Hello David. Now, what on Earth are you doing?
Conservator: I’m just doing a bit of sample preparation, with a paint sample, for it to be made into a cross-section to go under the microscope so that we can see the layers of paint on the sample that we have taken this from.
Narrator: Where is it? Where is the piece of paint?
Conservator: Have a look at the block, there is a very tiny spec of paint in there.
Narrator: It’s a piece of dust!
Conservator: It is actually the layers of an 18th century Italian painting in there. We’ve taken a very small sample. We have to decide very carefully where we’re going to take samples from and justify the reason for taking them. But we always try and choose areas of existing damage or cracks so that we can take the layer of painting without damaging anything fresh.
Narrator: So you take a tiny little spot and then you put it into those blocks. How do you put it into those blocks?
Conservator: Well what we have to do, is we have to make a little mould for the resin that we use, a clear polyester casting resin to actually embed these in and we make little blank bases, which are filled with resin here, half full, and then we carefully place the sample, when this is cured, on top of the base and then add further wet resin on top to encase the sample, then we let it cure. When its cured, we can begin to grind away the excess resin to get to the sample that we actually want, and that’s what I was doing on this machine here.
Narrator: But why can’t you just chop it, but it on a piece of slide and put it under the microscope?
Conservator: Well the difficulty is the size, these pieces are so fine, that you can’t really handle them. We also have to make sure that because we’re trying to get layers of paint in, you have to have them all aligned properly. If you are going to make a clean slice, you have to make sure that it is lying in the right way so that you can grind it correctly. And the block gives you a bit more to handle. The process I’m using is a wet process where we are doing a lot of the coarse grinding. For the fine grinding, when we get really close to the sample, we use a dry process where we use these sheets of impregnated fabric which are abrasive and come in various different grades.
Narrator: You can hardly feel anything.
Conservator: No, it’s very fine. It will polish resin like this to a mirror finish. It’s the sort of thing that is used in car factories to polish the cars after they have been painted. We get a very fine degree of finish on this.
Narrator: But then it doesn’t stop there, because then, this is I presume all the slides prepared?
Conservator: Yes, this what they look like when we put them under the microscope. When we have finished with the block, we attach it to one of these slides, these glass slides. We attach it using a very fine amount of wax and then we just push them together. Then, we can take it to the microscope to examine it.
Narrator: Now, how long does it take to go from having that tiny dot to being able to see what you want under the microscope?
Conservator: Well its quite a long process because taking the sample is quite and involved process and you have to concentrate to get the right sample in the first place. From laying out the block to setting up after its cured, you could be looking at about half a day, to three quarters of a days work and I’ve got, for instance, three other samples from the same painting, so it will take, to get the 4 samples, as much as three quarters of a day just to get the samples ready.
Narrator: Right then, I won’t keep you any longer, I’ll let you get on.
X-radiography in conservation
Narrator: Now David, to an untrained eye, that looks remarkably like a teddy bear to me.
Conservator: That’s interesting because it is an X-ray of a teddy bear. It’s a little Steiff teddy bear from about 1910 and we’ve x-rayed him to try and find out about the internal structure, whats inside him.
Narrator: Do you use x-rays a lot here, do you find them very useful?
Conservator: We do, its an extremely useful technique, you can gain all kinds of information about the internal structure, of how things are made, what they are made of and things that you just can’t see from the surface that might affect how you handle them, how they move or how you treat them.
Narrator: Now, he’s got something very interesting in his tummy, did you know that was there before the x-ray was taken?
Conservator: We suspected that there was something in this central area here, but we weren’t sure what. From the x-ray, we’re pretty sure that it is a little growling mechanism, so that if the growl was tipped over, he would make a little noise. Unfortunately, it doesn’t work anymore.
Narrator: Now, with X-rays, how useful are they for you, is it something that all museums have?
Conservator: Most museums will at least have access to them, however, what they don’t always have is access to digital ones like that which we have here. Traditionally it used to be done on a photographic wet process system with plates like these.
Narrator: That brings back memories of a broken arm, falling off a bike when I was a little girl.
Conservator: It’s exactly the same technology and the images are almost identical. In fact, the densities are also quite similar. The difference now is that we have this digital cassette, which still has a photosensitive plate inside, but its read by a laser in the machine, and the plate is reusable, so we’re not replacing film. It may be expensive initially, but in the long term, it’s cheaper.
Narrator: I suppose it is quicker as well?
Conservator: It is, it’s very much quicker. The thing we have found is that we would not necessarily have been x-raying such a variety of things, so easily because you can simply look whats there and you do not necessarily have to save the images. You also find that more people stand asking about looking into other things and want to find out about other things.
Narrator: Now, the kit you have here, its big and it can take teddy, but what happens if you wanted to x-ray something bigger?
Conservator: We’re obviously limited, in this instance here, with the size of the cabinet. If we have bigger items, we have another machine upstairs, which can x-ray much larger things, such as paintings, furniture or organic objects.
Narrator: We all hear about X-rays, and we think about x-ray specs, or being able to see things at the dentist, but what actually is an x-ray, how do we get those images?
Conservator: The image you see is generated by a machines of various sorts. The machines generate images electrically. X-rays are part of the electromagnetic spectrum just like light, they just happen to be at the other end of it and they have a very penetrative quality. Therefore, when we expose something to the rays, like teddy bear, the rays go through the different densities and those densities are represented onto the board below.
Narrator: Aren’t x-rays scary? I mean dentists, hide behind screens when they do them, are they not harmful here?
Conservator: Yes, they are still harmful here, but we take extra precautions the same as you would in the hospital. The machine we use, the cabinet machine, is extremely well shielded meaning that the rays do not come out of the cabinet when its in use. The larger machine that we use, we have a set of rules that we have to follow to make sure that nobody is exposed to radiation. That one is exposed in it’s own compound. There are a series of doors and locks and lights and bells to make sure that nobody is in there when the x-ray machine is on.
Narrator: So I can see why you’ve x-rayed Teddy here, to see whats inside him and whats he’s made of, but why would you x-ray something larger, for example a painting? What could you get from that, that you couldn’t get from say, a microscope?
Conservator: The x-ray provides a whole new level of information about internal structure and things that you can never see on the surface such as the underlying canvas that it is painted on, or where there may be old damages that may have an effect on the conservation treatment that is used. Similarly, with painting on wood panels, you can identify any woodworm holes, faults in the panel, any old joints or structures where you do not want to do any invasive treatment, and it can be used to decide what methods to choose.
Narrator: So you can use teddy and paintings or whatever, but are there any things that you would think, no you couldn’t use that?
Conservator: It depends on the information that you think you want. There is normally a reason, why you take the x-ray image of a particular object, there is a suspicion, an interest, there’s something there. The limitation is probably high-density metals and things that x-rays just cannot penetrate like lead, which is obviously a good example. But there are other things, for example some early paintings were done on mahogany wood, and mahogany is an extremely dense wood. So we can’t x-ray paintings that are done on mahogany. All you get is a very nice picture, of some fine grain wood. Also ivory, ivory is an extremely dense material, and for that reason, we can’t x-ray that. It’s a technique that can provide you with information that you haven’t got an also provide something without it being there.
Narrator: So teddy, with everything being there, does have a clean bill of health then?
Conservator: Yes, he has, except for his little growling problem.