Conservation of UK transport tokens
Many UK transport tokens are vulnerable to decay with time. Collectors should be aware of the dangers and store the tokens in an appropriate manner.
The Celluloid time-bomb
Celluloid, one of the first semi-synthetic plastic materials to be made, was launched (as Parkesine) in 1862 by Alexander Parkes, a Birmingham (UK) inventor. He made it by nitrating cellulose in the form of cotton wool to form cellulose nitrate then converted this into a mouldable material by adding plasticisers, especially camphor. His product was not successful and the world had to wait some 20 years until Hyatt (USA) and Spill (UK) and others perfected the mixture, its manufacture and the marketing of new products. By the turn of the century, thousands of plastic products were being sold across the world, most of them made from cellulose nitrate based celluloid or competitive materials in sheet form. Cellulose nitrate is highly flammable and many serious fires were started by celluloid getting too hot, especially in movie theatres when the celluloid film jammed in the projector, the heat of the bulb ignited the plastic and many lost their lives in the ensuing conflagration. Celluloid is also prone to degradation as it ages and many museum items and collectors' treasures have now crumbled away to a sticky, smelly disaster.
Celluloid was light in weight compared to metallic tokens, it wore relatively well and was low in cost and so celluloid was the first choice plastic for token producers for about fifty years and millions of them were made. Celluloid wasn't the only plastic material to be used by token and medallion manufacturers in the 19th Century, vulcanite was also used, especially in the USA, and several compositions based on wax, shellac, tree resins or gutta percha were patented from the 1840s onwards. We don't know precisely when celluloid was first used to manufacture tokens, but it was probably about 1885. However, its low cost and easy formability made it the 'standard' material for tokens up to the 1930s when the safer cellulose acetate and urea formaldehyde based materials took over.
By their very nature, celluloid tokens are doomed to degrade eventually and this has serious issues for the token collector. Over an indeterminate time, celluloid degrades at first slowly, giving off acidic gases, then it cracks and splits to a granular mess that has to be thrown away. This degradation process is progressive, it accelerates and is infectious because the off-gases stimulate degradation in nearby good quality Celluloid - hence it is described as the 'Celluloid Disease'.
Image shows a degraded 1d Wallasey transport token stored in a pocket in a regular pvc album page. This was perfectly ok last time it was checked, maybe 18 months before the picture was taken but the more worrying sight is that the adjacent 1½d token has started to decolourise - a tell-tale sign that the 'infection' has spread ! A hazy area is visible on the slotted pocket edge where the acidic fumes have condensed on the pvc, this haze is strongly acidic. Where celluloid tokens are stored in paper packets, these acidic fumes will cause the paper to crumble away.
High temperatures and high humidity accelerate the degradation and conversely, low temperatures and low humidity will slow it down. For collectors of plastic tokens this is a problem but to movie film curators it is critical, as most early films were shot on nitrate stock - the same material as celluloid and millions of feet of film have already been lost. To delay the inevitable, film archives store the movies in low humidity refrigerated containers with the atmosphere monitored for acidity, until such time as the images can be transferred to a more stable film stock. For tokens this might be unrealistic but there are good-housekeeping precautions that we can take. Firstly, the celluloid tokens should not be encapsulated as the gases, if trapped in the packaging, help speed-up the degradation process. Ideally they should be stored on non-acidic paper and ventilated to allow the gases to escape. Most museums now have indicator papers in the drawers where celluloid is stored, these are readily available and show colour changes in acidic fumes. Secondly, collections should be examined regularly and any affected tokens removed, to minimise 'infection'. Thirdly, the tokens should be stored cool, dark and dry, the cooler and drier the better!
Identification of the material from which the token was made is important too, celluloid is the only common plastic material with such speedy degradation, and unfortunately Smith describes most plastic tokens as 'Celluloid like' no matter what plastic they are made from.
There is one simple test that will help differentiate the various plastic materials commonly used from 1900 to 1960 and this is the hot-pin test. This involves, as the name suggests, heating a pin up to red heat and then gently applying it point first into the surface of the token and seeing what happens. One thing is certain, it will devalue the token considerably!
- Vulcanite gives off a brown smoke and smells somewhat of sulphur and rubber but not chokingly so. A better test is to rub the token with one finger covered with a cotton handkerchief which will slightly warm the vulcanite so that it gives off a sulphurous smell.
- Cellulose nitrate (celluloid) gives a puff of white smoke and a smell of camphor, if you are really unlucky the token will catch fire, conflagrate spectacularly and you will have discovered what it had been made from. the rubbing test will sometimes cause a smell of camphor to be emitted.
- Cellulose acetate was used from the 1930s, this will smell like vinegar in the hot pin test.
- Urea formaldehyde was commonly used from the 1930s, the hot pin will not penetrate the surface but will leave a brown mark.
- Polystyrene has been the most common token material since about 1960 as it is cheap and moulds good detail. Many grades will ring with a metallic sound if dropped on a hard surface.
- Polypropylene and Polyethylene have been used to make post 1950s tokens but as a material it is relatively soft. A common test is to gently push a fingernail edge against the rim edge of the token, this will leave a slight indentation.
If a plastic token was issued before 1930 it is almost certainly made from vulcanite or celluloid (exceptions would include vulcanised fibre). One alternative and better method of material identification is to use modern instrumental techniques such as FTIR which can easily positively identify cellulose nitrate and most other plastics.
It should be remembered that some token issuers replaced earlier celluloid tokens with similar ones in cellulose acetate.
Images of degradation in celluloid tokens
- 1 Wallasey 1D green 805BA stored in pvc pocket, severely degraded!
- 2 Southport 2D green 715BH, two tokens stored in the same packet, showing typical cuboid cracking inside the token - not a surface effect. The acidity has also caused a colour change in the affected area
- 3 Wolverhampton 3D pink 875BJ, the pink colour been changed under acidic conditions.
- 4 Aberdeen 1/2D transparent 30AN typical advanced cuboid cracking
- 5 Sheffield 2D green 685CH. Typical internal cracking
- 6 Wolverhampton 1D green 875BB
- 7 reverse of 6 showing typical internal crazing
- 8 West Bromwich 2 1/2 D Dark Green 840BD, note the rusty staples - acid attacks metals too!