What to monitor
Start with the variables that actually explain the risk.
For this material group, the environmental record is most useful when it captures the things below and keeps them tied to the object, space or display context.
- Relative humidity where salts or unstable glass are present
- Temperature for outdoor or freeze thaw risk
- Case and room differences for sensitive microclimates
- Visible light where decoration or mixed materials are sensitive
- Condition observations alongside the sensor record
What can go wrong
The number only matters because of the damage mechanism behind it.
Salt movement
Soluble salts can migrate and crystallise as moisture conditions change, leading to powdering, flaking or surface loss.
Unstable glass
Crizzled or weeping glass needs more careful humidity control than stable glass.
Composite surfaces
Paint, gilding, adhesives, fills and old repairs may be more sensitive than the ceramic, glass or stone body itself.
Published guidance
Useful examples, with the caveat kept attached.
Museums Galleries Scotland advises choosing an RH between 20% and 60% for ceramics, tiles and stone depending on embedded salts, with 20–30% given as an example where salts are active. Its general guide gives 40–60% RH for glass and notes that crizzled or weeping glass may need narrower control around 40%. For light, stone, ceramic, metal and glass sit in its relatively insensitive 300 lux group, provided there are no more sensitive decorations or components.
Where judgement comes in
Material labels can hide important exceptions. An excavated ceramic full of salts, a glazed object with unstable repairs and a sound modern ceramic are not the same conservation problem. Build the profile around the actual deterioration mechanism.
How this maps to LÆFAN
Keep the reason for the profile with the readings.
Use specialist profiles only where the object or collection justifies them rather than tightening an entire gallery unnecessarily.
Compare room and case conditions when a case is being used to buffer a salt sensitive or unstable object.
Keep condition notes and the profile rationale close to the monitoring record so future staff know why the tighter range exists.
For outdoor stone, use the monitoring record as environmental context but keep building fabric and freeze thaw assessment with the appropriate conservation specialist.
LÆFAN does not decide the conservation limit for you. It records the profile your institution has chosen, the source or rationale behind it, where it applies and what happened while it was in force.
Sources & further reading
Where the examples on this page came from.
Temperature and humidity in museums
Open source ↗Conservation and lighting
Open source ↗Choosing new display cases
Open source ↗Sources checked 6 October 2026. Guidance and standards can change, so follow the linked publisher page before adopting a value into policy.