Identifying plastics

Why identify the material?

It is good practice to identify the material of which an object is made because it enables you to understand more about the object. But it is vital for objects made of plastics as it will help you know how best to look after them.

All plastics degrade over time but some are much less stable than others. It makes sense to concentrate limited resources on providing objects made of these plastics with optimum environments or you might even decide not to collect such objects at all. To find out which materials these are go to Problem plastics.

The best way to learn to identify different plastics is to study a group of objects that already have the plastic from which they are made identified. That way you can get to know what they look, feel and smell like. Clues to help you know what to look for can be found at Identification: clues to get you started.

Identification can also involve sophisticated analytical equipment of which the Fourier Transform Infrared Spectrometer (FTIR) is the most widely used. Such machines can be brought to your museum at a cost. It does however require experts to carry out the analysis and opinions differ on its value.

For information on this and other forms of instrumental analysis please refer to Anita Quye and Colin Williamson ed., Plastics collecting and conserving, part two: analytical methods, pp.70 -73.

Clues to get you started

There will always be something you can glean from an object itself to help you decide what material it is made of or how it was manufactured. If you have any thoughts to contribute to the questions below click on them and find out how what you know may help. The notes attached to each question aim to help you make the most of what you know about the object to narrow down the options. Once you have done that you can go to the particular materials in the A –Z of plastic materials or the particular manufacturing processes in the A - Z of manufacturing processes to look in more detail at what you have decided are the probabilities.

When was it made?
What does it look like?
What does it feel like?
Does it smell?
What signs of deterioration can you see?
What marks are on it?

 

When was it made?

If you have an idea when the object was made, use the information under the relevant date span to narrow down the probabilities. Bear in mind though what you are getting are probabilities not certainties. Many plastics have had long periods of gestation and, as more and more plastics are invented, some become outmoded but nonetheless stay in production. And, although some materials are used most often with a particular manufacturing process, they may also be used from time to time with another. If you have a hunch that an object is made of a particular material outside the dates given or manufactured in a different process go to the material or process in the A–Z guides to check out what is possible in greater detail.

1840-1880
1880-1915
1915-1925
1925-1940
1940-1950
1950-1965
1965-onwards

 

 

1840-1880

Materials
Manufacturing processes 

 

1880-1915

Materials Manufacturing processes
Cellulose nitrate Blow moulding, fabrication, thermoforming
Shellac Compression moulding
Vulcanised rubber Compression moulding, fabrication, turning

 

1915-1925

Materials Manufacturing processes
Casein formaldehyde Fabrication, extrusion
Cellulose nitrate Blow moulding, fabrication, thermoforming
Phenol formaldehyde Compression moulding, casting
Shellac Compression moulding
Vulcanised rubber Compression moulding, fabrication, turning

 

1925-1940

Materials Manufacturing processes
Casein formaldehyde Extrusion, fabrication, thermoforming
Cellulose acetate Compression moulding, fabrication, injection moulding
Cellulose nitrate Blow moulding, fabrication, thermoforming
Phenol formaldehyde Compression moulding, casting
Urea formaldehyde Compression moulding
Shellac Compression moulding

 

1940-1950

Materials Manufacturing processes
Cellulose acetate Fabrication, injection moulding
Phenol formaldehyde Compression moulding, casting
Polyamide Casting, extrusion, injection moulding
Polymethyl methacrylate Casting, extrusion, fabrication, thermoforming
Polythene Extrusion, blow moulding, injection moulding
Urea formaldehyde Compression moulding

 

1950-1965

Materials Manufacturing processes
Acrylonitrile butadiene styrene Injection moulding
Glass-reinforced plastic Compression moulding, fabrication
Melamine formaldehyde Compression moulding
Phenol formaldehyde Compression moulding
Polyamide Casting, extrusion, injection moulding
Polymethyl methacrylate Casting, extrusion, fabrication, injection moulding, thermoforming
Polypropylene Blow moulding, injection moulding, casting
Polystyrene Extrusion, foaming, injection moulding
Polythene Extrusion, blow moulding, rotational moulding
Polyurethane Blow moulding, extrusion, injection moulding, foaming
Polyvinyl chloride Blow moulding, extrusion, injection moulding, foaming, rotational moulding
Silicones Injection moulding

 

1965 onwards

Materials Manufacturing processes
Acrylonitrile butadiene styrene Injection moulding
Glass-reinforced plastic Compression moulding, hand lay-up, fabrication, pultrusion, vacuum laminated
Phenol formaldehyde Compression moulding
Polyamide Casting, extrusion, injection moulding
Polycarbonate Blow and injection moulding, extrusion, foaming
Polythene Blow moulding, extrusion, injection moulding, rotational moulding
Polypropylene Blow and injection moulding, casting (film)
Polyethylene terephthalate Blow moulding, extrusion, injection moulding
Polymethyl methacrylate Casting, extrusion, fabrication, injection moulding, thermoforming
Polystyrene Extrusion, foaming, injection moulding
Polyurethane Blow moulding, extrusion, foaming, injection moulding
Polyvinyl chloride Blow moulding, extrusion, injection moulding, foaming, rotational moulding
Silicones Injection moulding

 

What does it look like?

Is it:

 

Transparent

Relatively few plastics are transparent like glass. All transparent plastics can be made translucent or opaque by the addition of pigments or fillers. Some plastics are only transparent in sheet form. If it is moulded and transparent it is probably made of one of the following:

Phenol formaldehyde as liquid resin not with filler
Polycarbonate
Polylactide
Polyethylene terephthalate
Polymethyl methacrylate
Polyurethane

The following plastics can also be clear in sheet or film form but are translucent or opaque when injection-moulded:

Cellulose acetate
PVC
Polypropylene

Is it translucent?  If so, it can be any of the above and also:

Polythene
Silicones

 

Pale or brightly coloured

If so it is unlikely to be made of one of the following as they usually come in dark colours. However plastics that can be light or bright in colour also come in dark colours.

Bois durci
Gutta percha
Vulcanised rubber
Horn
Phenol formaldehyde as liquid resin not with filler
Shellac

 

Amber, ivory, tortoiseshell, or pearlised

If it imitates one of these it is likely to be made of one of the following:

Casein formaldehyde
Cellulose acetate
Cellulose nitrate
Phenol formaldehyde as liquid resin not with filler

 

Shiny

If it has a hard glossy surface it is likely to be one of the following but bear in mind that nowadays almost any plastic can be made glossy:

Acrylonitrile butadiene styrene
Casein formaldehyde
Melamine formaldehyde
Phenol formaldehyde
Polycarbonate
Polymethyl methacrylate
Polystyrene

 

What does it feel like?

Soft

Some plastics have such a soft surface that they can be indented with a finger nail. If the object feels as if that is likely it is probably made from one of the following:

Polythene
Polyurethane
Polyvinyl chloride (when in flexible form)
Silicones

Flexible or rigid

Many plastics can be rigid or flexible however a few are always rigid. These are:

Acrylonitrile butadiene styrene
Bois durci
Gutta percha
Phenol formaldehyde
Vulcanised rubber

 

Sticky

Stickiness is a sign of degradation. The following can go sticky:

Cellulose acetate
Cellulose nitrate
Polyvinyl chloride
Polyurethane foam

 

Does it smell?

The following smells are sometimes given off by the plastics listed:

Carbolic acid: phenol formaldehyde
Formaldehyde: casein formaldehyde
Milky, if rubbed: casein formaldehyde
Mothballs (camphor): cellulose nitrate
Plasticky (new car smell): polyvinyl chloride
Sweet: polyvinyl chloride but only when degrading
Sulphurous: vulcanised rubber
Vinegar: cellulose acetate
Vomit /rancid butter: cellulose butyrate, cellulose acetate butyrate
Waxy: polythene

 

What deterioration is there?

The following signs of deterioration are associated with the materials listed:

Bloom

This takes the form of a white powder that can be wiped off or a pale mistiness.

Cellulose acetate
Cellulose nitrate
Polyvinyl chloride

Cracks and splits

Casein formaldehyde
Cellulose nitrate
Phenol formaldehyde
Polycarbonate
Polystyrene
Polyvinyl chloride
Shellac
Urea formaldehyde

Crazing

Casein formaldehyde (surface crazing)
Cellulose nitrate (internal crazing)
Gutta percha (network of small cracks on surface)
Polymethyl methacrylate
Polystyrene
Urea formaldehyde (an orange peel effect)

Crumbling

Gutta percha
Polyurethane foam

Embrittlement

Polyvinyl chloride

Fading and discolouration

Pigments can fade independently, leading to complete changes of colour.

Phenol formaldehyde, also dulls
Polyamide, tendency to yellow
Polymethyl methacrylate, sometimes discolours in light
Polyvinyl chloride: yellows and goes brown
Polyurethane: yellows
Urea formaldehyde, also dulls
Vulcanised rubber, often has a yellowish brown tinge

Physical distortion, warping

Cellulose acetate

 

 

What marks are on it?

A small bird’s wing was used to indicate the use of the material bois durci.

An infinity sign is the logo of Bakelite and thus frequently indicates the material phenol formaldehyde but the company made many other plastic materials. It only appears on Bakelite promotional mouldings. Bakelite did not make mouldings for the general market.

Recycling triangles were introduced in 1988 so any object with these on must date from that year or later.

Smooth circular marks are a sign of the use of ejector pins to push the moulding from the mould and thus of injection moulding.

An imperfection on an otherwise smooth surface may be a residue left at the spot the material has been forced into the mould and thus indicate the use of injection moulding. Such marks can be extremely hard to detect and they may not be where you might expect to find them, for example centrally placed on the base or on the edge. They can be polished off so their absence does not tell you anything.

The following are trade names that frequently appear on mouldings. They are associated with the materials indicated:

 

Bandalasta Thiourea-urea formaldehyde
Beetleware Urea formaldehyde
Carvacraft Phenol formaldehyde
Gaydon Melamine formaldehyde
Linga Longa Urea formaldehyde
Melaware Melamine formaldehyde
Melmex Melamine formaldehyde
Xylonite Cellulose nitrate

< What are plastics

Plastics timeline >