STATE OF CONSERVATION

The polyethylene is broken in several places in the bottom corners.
The beeswax displays several nail marks and is peeling away from the support in several places.

Sample reference number: 1462: 1462

Sample description:
The sample includes two drawing pins covered with an intense blue paint. The aim of the analysis is to determine the composition of the paint.

Analysis:
The sample was analysed under a scanning electron microscope (SEM) and using Fourier transform infrared (FTIR) spectroscopy. The findings of these analyses show that cobalt blue was used as the pigment and beeswax was used as the binder.

SEM image of this paint's appearance

Characteristics of the material, Polyethylene

Polyethylene

"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. Ethylene polymers are used as hot adhesives, packaging laminates (...).
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 (...)."

"(...) Polyethylenes are susceptible to photo-oxidation when exposed to ultraviolet light. This form of degradation is autocatalytic and once initiated proceeds at an accelerating rate (...). The first sign of deterioration is generally yellow or brown discoloration, sometimes in blotches. This is followed by a loss of mechanical properties so that cracking may result when the material is flexed. Early colorants fade badly when exposed to strong light, especially if any ultraviolet is present. Black or dark opaque colours are more stable than translucent or pale colours, due to the action of colorant in filtering the light. High density polyethylene is theoretically more resistant to photo-oxidation than low density, but in practice the difference is small (...)."

Characteristics of the material, Wax:

Discoloured beeswax:
Animal-origin wax. It is a long-chain fatty acid sterified with long chain alcohols. It is solid and practically insoluble in water, but is more permeable to water vapour. Soluble in aromatic hydrocarbons and chlorates, and in hot ethanol. It is very sensitive to temperature changes.
Beeswax is chemically very stable and of a lipoid nature.
It contains:
- Saturated hydrocarbons
- Saturated hydroxyacids or acids
- Alcohols, monols and diols

CONCLUSIONS

No visible alterations due to exposure to light on the polyethylene surface were found. However, we are aware of the fact that despite being a relatively stable material, it is susceptible to photo-oxidation when exposed to ultraviolet light.