杏吧原创

鈥淲E SEE her as having donated her body to science,鈥� says Anita Quye, glancing
across at the sad little figure on her lab bench at the Royal Museum of Scotland
in Edinburgh. The body, a modest 40 centimetres high, stank of vinegar when it
arrived. Now, the smell has subsided and the autopsy is in full swing.

The body is that of a plastic doll dating from around 1940. Her arms and one
leg are shrivelled and discoloured. The other leg, like her head, is still
bright pink. 鈥淚t鈥檚 a puzzle why one leg is different from the other,鈥� says Quye,
an analytical research chemist at the National Museums of Scotland and
coordinator of the international Historical Plastics Research 杏吧原创s鈥�
Group.

The vinegar smell is a dead giveaway though, caused by traces of acetic acid
vapour seeping from the cadaver. Like many dolls from the same era, she is made
from cellulose acetate, one of the plastics developed in Victorian times that
ushered in our synthetic century. Vinegar is the telltale smell of death,
produced as the acetate plastic disintegrates. 鈥淚t鈥檚 a 20th-century
tragedy,鈥� says Quye. 鈥淚t鈥檚 caught us out because we didn鈥檛 expect it.鈥�

That tragedy goes beyond plastic dolls. Toy trains and planes fashioned from
metal alloys, platoons of plastic soldiers, classic teddies, even table football
players, are all slowly decomposing in the attic. Not even our images of bygone
Christmases are safe, with videotapes less than a decade old on the danger
list.

Museums are realising that the paraphenalia of the 20th century is falling
apart鈥攁nd fast. Icons of the modern materials revolution in museum
collections are at risk, from plastic food containers to spacesuits worn during
the Moon landings.

Conservators are frantically trying to work out how modern materials
deteriorate chemically, how fast and how irreversibly. 鈥淧lastics are just
beginning to degrade now, and we鈥檙e trying to understand the underlying
principles,鈥� says Brenda Keneghan, a chemist studying modern materials at the
Victoria and Albert Museum in London. So far, she鈥檚 identified 8000 items in the
museum鈥檚 collections that contain plastics, and the list is growing. 鈥淭here鈥檚 a
wide variety, and they all degrade according to their own chemistry,鈥� she
says.

Nowhere is the growing damage more evident and varied than in toy
collections. Plastic-doll disease has already affected many period dolls made
from cellulose acetate, a semi-synthetic polymer made by treating cellulose
from natural materials such as cotton and wood with sulphuric and acetic acids
and acetic anhydride.

Not surprisingly, plastics manufacture was cruder in Victorian times than it
is now, and impurities in the material are beginning to make their presence
felt. Lurking sulphates and nitrates turn into acids which attack cellulose
acetate polymer chains and make them brittle. Acetate groups degrade to produce
the acetic acid that gives the rotting plastic its telltale smell.

To make matters worse, plastic-doll disease is contagious, spreading from
doll to doll. The degradation process is catalysed by acid, and the acetic acid
fumes from the infected dolls can trigger the disease in neighbouring 鈥渉ealthy鈥�
dolls. No cure exists yet.

Dolls made from a sister material鈥攃ellulose nitrate 鈥� date back
even further but suffer a similar fate. In this case, the acids knock off
nitrate groupings, which are converted into nitrogen oxide gases. The material
reverts to rigid cellulose, causing cracks and again making it brittle.

Turning green

The acid impurities also dissolve metal parts in dolls, such as spigots and
hinges in the head, producing fluids that stain the plastic. Earlier this year,
a team of chemists at the University of Bradford unravelled some of the
chemistry behind this form of the disease, which can make dolls cry thick brown
tears containing iron oxide. 鈥淭here鈥檚 a public perception that plastics last for
ever, but they don鈥檛,鈥� says Howell Edwards, the chemist who led the team (see
Technology, 4 May, p 17).

So far, classic dolls made from cellulose acetate or nitrate have been the
worst affected by plastic-doll disease. But there are signs that more modern
dolls are beginning to suffer, too.

Barbie dolls made from polyvinyl chloride (PVC), for example, are at risk. 鈥淎
real problem with Barbies is copper staining from armbands and earrings,鈥� says
Kim Nissan, a conservator who works closely with Quye. Nissan collects Barbie
dolls as a hobby, and is seeing signs of degradation. 鈥淵ou often see examples of
this green staining with verdigris,鈥� she says, especially on the face. She says
that some collectors have tried treating the green areas with anti-acne lotions
that bleach it. 鈥淕reen鈥檚 really disfiguring, so it鈥檚 better if it鈥檚 bleached,鈥�
she says, although as a conservator she does not recommend it. 鈥淲e do not know
what the bleach is doing to the plastic.鈥�

California-based Mattel Toys, which makes Barbie dolls, says that the company
now coats the copper jewellry with nickel to prevent staining. Nissan says that
she鈥檚 also seen opaque spots appearing on some Barbies. She suspects that the
dolls might be sweating out compounds used as fire retardants and as stabilisers
for the plastic. Mattel says that traces may appear at times, but even if they
do they will not accelerate deterioration of the dolls.

Even the cardboard boxes used to store the Barbies pose a threat because they
give off a mixture of formic and acetic acids which come from the soft woods
used to make them. These can react with the plastic, causing degradation. The
irony, says Nissan, is that early Barbies can be worth more in unopened boxes.
鈥淥nce you open the box, they lose value,鈥� she says. And that鈥檚 no small
consideration: Barbies dating back to 1959, the year the line was launched, can
fetch $10 000 in the US, where they鈥檝e become collectors鈥� items. 鈥淔rom a
conservation point of view, it鈥檚 difficult to know what to do, because
conservators would advise keeping doll and box separate,鈥� says Nissan.

Cabbage Patch dolls, one of the big must-buys of the 1980s, have also hit
problems. 鈥淚n some batches, the PVC was contaminated with metal dust, which
reacts with PVC to make hydrochloric acid,鈥� says Mary Baker, a veteran and
pioneer of modern materials conservation at the Smithsonian Institution in
Washington DC. 鈥淚n some dolls, it bleached out clear, and the dolls got white
spots, like reverse measles.鈥� Mattel, which also makes Cabbage Patch dolls, says
that the strict quality control measures employed today make similar
contamination incidents unlikely.

Modern teddy bears, notably those made in the 1960s, are facing a different
kind of sticky end. The plastic yellow foam chips used to stuff Ted have, over
the past three decades, mysteriously turned to red powders and goo. The powder
is slowly released through the skin of the bear, but turns into red goo on the
inside of the seams. No one yet knows why.

Luckily, says Yvonne McGeehan, who runs a teddy bear hospital in Britain,
these can be turned inside out, washed clean and refilled with polyester fibre
stuffing routinely used in duvets and pillows today.

Not that any amount of stuffing could help Action Man, the doll-sized
polyethylene soldier that celebrated his 30th birthday this year. In the 1970s,
some Action Men were equipped with rubber hands, but these have oxidised and
become brittle, causing fingers to snap off, says Peter Evans, editor of
Plastic Warrior magazine and a keen collector of Action Men. Nowadays,
plastic moulding techniques and quality control are much more sophisticated at
Action Man鈥檚 makers, Hasbro of Pawtucket, Rhode Island. The firm says that these
problems are now seldom seen.

At the tiny end of the military scale, platoons of centimetre-high
polyethylene soldiers sold in the 1960s are now flagging badly. Evans says that
Airfix, the company that made the soldiers, put banana oil with the polyethylene
to make it easier to remove the soldiers from their moulds. They also added
French chalk to the mixture to absorb moisture. But the French chalk has dried
the soldiers so much that they are becoming brittle. 鈥淵ou can crush them to dust
between your thumb and forefinger,鈥� says Evans. 鈥淭he only thing you can do is
coat them with varnish or polyvinyl acrylic glue,鈥� he says.

Back in the grown-up world, many other 20th-century items are falling into
disrepair through deterioration of modern materials. They include sealable
plastic food containers made of polyethylene, rubber parts of NASA spacesuits,
rubber bands in catapults and rubber snorkelling masks.

And works of art are not immune. Polymethylmethacrylate sculptures by the
20th-century American artist Naum Gabo are being restored at the Sainsbury鈥檚
Centre of modern art in Norwich. And a few hundred kilometres away, a set of
polyethylene hair curlers is slowly disintegrating in an exhibit called
Supermarket lady on show in the Ludwig Forum in Aachen, Germany.

More alarmingly, all the Christmas memories of millions of people stored on
home videotapes are rapidly deteriorating. 鈥淚f your tapes are more than five
years old, get them copied now,鈥� says Baker at the Smithsonian. The tapes are
made with a base of polyester, which is durable but which can stretch and then
shrink if subjected to heat. The videotape images are recorded in magnetic
particles laid down on the polyester in a polyurethane rubber binder. But over
time, the binder loosens and becomes less like rubber and more like paste.

鈥淚t starts to soften and rubs off on the playing head,鈥� says Baker. As a
result, the images are ruined. 鈥淭he first sign of damage is that the video looks
fuzzy, with `snow鈥� in the picture,鈥� says Baker. The best thing to do, she says,
is take it to a specialised copier of tapes and get two fresh copies recorded,
one for showing and the other for storing as a 鈥渕aster鈥� version. Her other piece
of advice is to take the video out of the machine and store the tape immediately
after use, to avoid exposing it to heat in the video player. 鈥淒on鈥檛 leave it on
the TV either, which is even warmer,鈥� she says.

Juggling memories

Most galling is that there is still no satisfactory medium for archiving.
鈥淚t鈥檚 not like the days when you had black and white photos that lasted for
ever,鈥� says Baker. 鈥淲e鈥檝e got to live through a period of trying to juggle our
memories, and though the advice about degrading videotapes may be unwelcome,
I鈥檒l be happy if it saves people from losing something important.鈥�

Meanwhile, at the British Museum, Yvonne Shashoua has discovered a way of
preserving rubber using sachets of iron filings. The product, called 鈥淎geless鈥�,
was developed in Japan by Mitsubishi to stop biscuits going mouldy. The iron
filings in the sachets draw oxygen from the air to form iron oxide. This
prevents it reacting with the rubber and causing ageing. 鈥淏ut we can only slow
down, not stop deterioration,鈥� says Shashoua.

Chemists such as Quye and Keneghan share this view, and believe that
prevention is preferable to cure, which has its own dilemmas. 鈥淪hould we try and
stop such items falling apart?鈥� asks Quye. 鈥淚f we repair things with a modern
plastic, will it react with the original and ruin it?鈥�

But the large number of plastics used to make our artefacts makes even
prevention a difficult task. Through a collaborative research project with the
chemistry department of the University of Strathclyde, Quye is hoping to develop
tests that will warn of problems to come. To give people a chance to save their
favourite toys for future Christmases, Quye will be running a 鈥減lastics clinic鈥�
at the Edinburgh International Science Festival in April next year. By analysing
a sample, she and her colleagues hope to identify just which plastics they are
made from. Then, they can offer advice on storage conditions, such as light and
humidity, that will minimise damage. 鈥淲e鈥檙e trying to anticipate problems,鈥� she
says.

Meanwhile, until they work out their dolls鈥� chemistry, collectors such as
Nissan will live in fear of plastic-doll disease, scared that simply cleaning
their treasures will expose them to countless evils. 鈥淓ven the hair is plastic,鈥�
says Nissan, 鈥渟o I鈥檝e never shampooed it.鈥�

* * *

Planes, trains and automobiles

Plastics are not the only materials affected by degradation. As the infantry
crumbles, its air cover is disintegrating on the runway, grounded by 鈥渨ing
droop鈥�, a problem in 1930s model aeroplanes made by the Meccano company in
Liverpool.

Equally affected were the company鈥檚 early Dinky cars and Hornby trains. It鈥檚
all down to 鈥渓ead rot鈥�, a metallurgical problem. From the mid-1930s, Meccano
began making toys from a zinc-based alloy called Mazak. The material moulded
well, and brought out finer detail than the lead it replaced. By weight, Mazak
contained 3 to 4 per cent aluminium and 1 to 2 per cent copper. But traces of
lead as low as 0.008 per cent or cadmium as low as 0.006 per cent spelt disaster
for the toys.

鈥淭hey used to throw lead-contaminated shavings into the pot with the zinc,鈥�
says Arthur Clapp, a restorer in the Wiltshire town of Warminster, who
specialises in the repair of Meccano toys and trains. The lead atoms migrated to
the grain boundaries in the zinc alloy, causing a change in the crystal
structure, leading to a swelling of up to 10 per cent in these areas. Cracks
appeared in the models as a result of this expansion, and ultimately they would
flake apart, turning to dust.

According to Clapp, the planes were worst affected. 鈥淭he wings would curl
up,鈥� he says, a result of uneven grain boundary swelling. Cars made almost
completely from Mazak turned to dust, as did Mazak wheels on Hornby trains built
just before the Second World War.

鈥淗ornby wheels literally disintegrated, but the superstructure of the
locomotive was made from pressed tinplate, which was unaffected,鈥� says Simon
Goodyear, a restorer of toy cars and trains based in Huddersfield. 鈥淚鈥檝e had
locomotives pristine in terms of their paint and bodywork, with wheels that had
crumbled in the box,鈥� he says.

During the Second World War, Meccano was requisitioned to perform quality
pressure die-casting for the Ministry of Defence. 鈥淕iven the necessity to work
to ministry specifications, there was tighter quality control and the company
learnt how to craft Mazak to perfection,鈥� says Goodyear.

After the war, Dinky cars were made of Mazak or Mazak-like alloys, but lead
rot was consigned to the history books through Meccano鈥檚 newfound expertise in
manufacture which, according to the company, persists to the present day.
Understandably, intact models from the 鈥渓ead-rot鈥� period are unusually valuable,
says Goodyear.