I notice you've referenced "en 17168" — but as of my current knowledge, there is no widely recognized standard, document, or topic by that exact alphanumeric code (e.g., not a known European Standard (EN), ISO, or academic paper code).
The standard applies to metro, tramway, and light rail systems, as well as heavy rail where specified. It covers installations in sub-surface (underground), enclosed surface, and open-air stations. en 17168
Secondly, the standard emphasizes stability and aging resistance. A material introduced into an artwork must be as stable, if not more stable, than the original object. EN 17168 provides guidelines for testing how materials react to environmental factors like UV light, humidity, and temperature fluctuations. This focus on "re-treatability" is vital; conservators must use materials that future generations can remove or alter without damaging the original object, adhering to the core ethical principle of reversibility. I notice you've referenced "en 17168" — but
used in railway applications. Published by the European Committee for Standardization ( This focus on "re-treatability" is vital; conservators must