STATE OF CONSERVATION

The paper displays spots of oxidation due to the glue used to stick it to the plywood support.
Some glue stains can be observed on the polypropylene.
The display cabinet is eroded in several places.

A powerful petrochemical industry developed in Italy after the Second World War and, as result, so did a major plastics industry. Within that context, Giulio Natta and his team of scientists at the Milan Polytechnic discovered polypropylene. That discovery earned them the Nobel Prize in 1963.
Polypropylene is a synthetic propane polyolefin. Its general formula is:

It is obtained by polymerisation with propane catalysts. The type of catalyst used is the Ziegler-Natta one, since polymers obtained by that method have better physical properties than those obtained by other methods.
molecular weight: 50,000 (average)
density: 0.9
melting point: 170°C
solubility: it is insoluble under 80°C in water and usual organic solvents
mechanical properties: similar to high-density polyethylene at low temperatures

"POLYETHYLENES (PE) are thermoplastic polymers belonging to the polyolefin group. They are obtained by the polymerisation or copolymerisation of olefins such as ethylene or propylene. Polypropylene is used to make transparencies (...).
Compounds containing more than 1,500 carbons contain phthalates and are used to make packaging bags and in the paper lamination process because they are very impermeable to water and ambient humidity.
The properties of polyethylenes depend on their degree of polymerisation and crystalinity. They age by photo-oxidation, form three-dimensional nets and discolour (...)."

"Polypropylene:
Catalysts which promote the polymerisation of propylene were developed in Italy in 1954 and were used in the commercial production of polypropylene which started in 1959. (..)
Polypropylene is more susceptible to photo-oxidation than polyethylene and more attention is given to stabilisation, specially for exterior applications (...)."

Paper: a plant-origin material basically composed of cellulose fibres. "It is a natural offset paper. However, it is usually drier, particularly when used in hot laser photocopiers or high-output photocopiers that print on both sides to prevent curling problems."

Manufacture: chemical pulp
"As the name suggests, chemical pulp is obtained by chemically treating wood to completely remove some of its components, basically lignin. The more energetic the wood-cooking process, the greater the degree of lignin removal."
Products supported: dry ink or toner.

Sample 1 was shielded from light and the observations made under an optical microscope did not determine any visible deterioration in the paper, as suggested by the fact that there were whole fibres and no significant separation. No alteration or yellowing of the paper was found. During the staining of the paper fibres, the probable origin of the paper was determined: chemical pulp with whole fibres from dense or resinous plants. No significant alteration was found.

Sample 2 was shielded from light and the observations made under an optical microscope determined the existence of yellow stains probably associated with the presence of some type of glue sticking the paper to the base. Those stains are located on the edges of the paper. Chromatic evolution is good and shows signs of a minor decrease in luminosity of less than 2%.

Colour analysis:
The readings were taken from black and white areas, and from areas of both those colours that were exposed to light and shielded by the frame forming part of the work. The following table shows the data for the readings taken from this work.

Readings:

The diagram on the next page shows the diffuse reflectance curves obtained at each of the mentioned points.

The readings correspond to all achromatic (colourless) points, as indicated by the low saturation values calculated (excitation purity). The following comments can be made about the numeric data:

1. Readings taken from the white areas show a chromatic evolution that is characteristic of ageing paper: yellowing of its organic compounds. The shielded area has greater luminosity, less excitation purity (more colourless) and a shorter dominant wavelength.
   
   
2. Readings taken from the black areas show a similar evolution, even though luminosity evolves in the opposite sense: less luminosity in the shielded area, meaning "blacker" than the exposed area affected by light.

Therefore, it can be deduced that some yellowing of the paper used as the support has occurred in the black and white areas, and that the black colour has faded, which is demonstrated by an increase in luminosity. In other words, the whites have become yellower and the blacks have become greyer, with yellowing of the background that is visually unnoticeable because of the low luminosity caused by the black pigment.

Absolute Data for Diffuse Reflectance at Each Reading Point

Sample reference number: 507-A

Sample description:
The sample is a piece of slightly warped paper photocopied on one side. The aim of the report is to evaluate its state of conservation. It should be mentioned that this fragment is usually shielded from light.

Analysis:
The observations made under an optical microscope did not determine any visible deterioration in the paper, as suggested by the fact that there were whole fibres and no significant separation. However, there was probably less toner (the ink used to make photocopies) than at the time it was made.
No alteration or yellowing of the paper was found, as indicated in greater detail in the report on chromatic stability. On the other hand, during the staining of the paper fibres, the probable origin of the chemical pulp was determined (fibres from leafy and resinous plants). No significant alteration was found.

Optical microscope image of this paper sample's fibres

Detail of a resinous plant fibre

Sample reference number: 507-B

Sample description:
The sample is a piece of paper slightly photocopied on one side. The aim of the report is to evaluate its state of conservation. It should be mentioned that this fragment is usually shielded from light.

Analysis:
The observations made under an optical microscope determined the existence of yellow stains probably associated with the presence of some type of glue for sticking the paper. Those stains are located on the edges of the paper. However, the general state of this paper is good. Chromatic evolution, as indicated in the report on this issue, is good, and shows signs of a minor decrease in luminosity of less than 2%. On the other hand, it would be worth doing further analyses to corroborate more exhaustively the state of the paper in more specific areas.

Optical microscope image of this paper sample's fibres

Sample reference number: 507-C

Sample description:
The material was analysed using Fourier transform infrared (FTIR) spectroscopy.
Ultraviolet radiation in plastic materials has enough energy to produce photochemical reactions and even break molecular links if the wavelength is low enough (high energy).
The maximum sensitivity of polypropylene is reached at 370 nm. However, if the composition is uneven, spectral sensitivity has a wide wavelength interval. So, for polypropylene, somewhere in the region between 300 and 400 nm is considered sufficient to break C-C and C-H links.
In fact, light stability of polypropylene is not generally very good unless it has been modified by adding UV stabilisers.

CONCLUSIONS:
Regarding the polypropylene of this work, we were able to determine that there were no significant alterations. Despite that, we must be very careful with the light since it is very sensitive and susceptible to photo-oxidation when exposed to light.
Regarding the paper, it can be deduced from the chromatic analyses that some yellowing of the paper used as the support has occurred in the black and white areas, and the black colour has faded, which is shown by an increase in luminosity In other words, the whites have become yellower and the blacks have become greyer, with yellowing of the background that is visually unnoticeable because of the low luminosity caused by the black pigment.