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, especially in sealed cases
- Temperature alongside RH to understand local conditions
- Evidence of condensation or water ingress
- Pollutants and case materials as separate corrosion risks
- Condition of corrosion products and salts
What can go wrong
The number only matters because of the damage mechanism behind it.
Active corrosion
Moisture and salts can drive corrosion. Lower RH can be critical for unstable archaeological metals.
Mixed materials
A metal object may include wood, leather, textile, enamel, paint or adhesives, so an RH chosen for the metal alone may not suit the whole object.
Case chemistry
Sealed cases can help create a dry microclimate, but unsuitable case materials and pollutants can also accelerate corrosion.
Published guidance
Useful examples, with the caveat kept attached.
Museums Galleries Scotland advises that mixed metal collections should be kept below 65% RH and generally benefit from drier conditions. Its broader temperature and humidity guide says unstable or corroding metals may need conditions as low as 10% RH. For archaeological material it specifically states that iron should be kept very dry, below 15% RH. Historic England also notes that iron corrosion is retarded below about 15% RH.
Where judgement comes in
Those very dry figures are specialist cases, not a target for every metal object. Stable historic metal, composite objects and treated surfaces can have different needs. If corrosion is active, the profile should follow a conservator’s assessment of that object or group.
How this maps to LÆFAN
Keep the reason for the profile with the readings.
Use a case or enclosure as its own monitored environment when the dry microclimate matters more than the room.
Keep the profile source visible so a 10–15% RH target is clearly identified as a specialist conservation decision rather than a generic museum default.
Compare case and room readings to spot loss of environmental buffering or a failing seal.
Use alerts for sustained excursions rather than reacting to every brief sensor wobble in isolation.
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.
Caring for metal collections
Open source ↗Temperature and humidity in museums
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.