Arid

This climate is generally very dry, however, in arid areas it is often very hot during the day and very cold at night. This wide fluctuation in temperature is matched by wide fluctuations in relative humidity, for example from 75%–20%RH in a day.

When caring for photographs in arid areas it is important to note that:

• insects can still survive;

• paper and photographic emulsions tend to give out the water they contain - this can lead to the photographs becoming dry and brittle; and

• as they release moisture at different rates, the paper and emulsion can begin to separate.

Remember that even arid areas can have periods of higher relative humidity, even though the periods may only be very short.

The system of layers of storage—wrappers, boxes, boxes within cupboards—is particularly suited to arid areas because of the tendency to get quite marked fluctuations in temperature and relative humidity. Many arid areas are also very dusty and so the layers of storage protect the photographs from dust and grit.

Because of the large temperature fluctuations in arid areas, there is a risk that condensation could form inside plastic wrappers, leading to sticky emulsion and possible mould growth.

Note: If your photographic collections have been stored in an arid environment for a considerable period and they are stable—do not try to alter the environment to meet the recommended ideal conditions. This could do more harm than good. The emphasis should be on long term stability.

Temperate

A temperate climate is considered a moderate climate, however, temperate climates tend to have a greater range of temperatures than tropical climates and may include extreme climatic variations.

• It is probably easier to come close to the recommended ideal conditions for the storage of photographs in a temperate climate, however, it is unlikely that you will be able to maintain an even environment without the help of sophisticated air conditioning equipment.

• The system of layers of storage - wrappers, boxes, boxes within cupboards will be very useful in helping to buffer against the extreme conditions that can occur in a temperate environment.

• As for all climatic areas, regular inspection of storage and display areas is important so that developing problems do not go unnoticed.

Note: If your photographic collections have been stored in a temperate environment for a considerable period and they are stable—do not try to alter the environment to meet the recommended ideal conditions. This could do more harm than good. The emphasis should be on long term stability.

Tropical

These climates are characterised by heavy rainfall, high humidity and high temperatures.

When caring for photographs in high humidity conditions it is important to note that:

• insects and moulds thrive and reproduce readily.

• the rate of deterioration due to light and UV radiation increases.

• different components of single objects will take up moisture at different rates and swell by different amounts—this can lead to problems such as emulsions separating from the photographic base paper.

• gelatine emulsions on photographs swell and can readily stick to anything they are in direct contact with.

Remember that in tropical areas, air flow is important and this should be taken into account when designing storage and display systems.

The use of plastic sleeves for storage and display is not recommended in tropical areas, as the sleeves restrict air flow and will prevent damp photographs from drying out.

Note: If your photographic collections have been stored in a tropical environment for a considerable period and they are stable—do not try to alter the environment to meet the recommended ideal conditions. This could do more harm than good. The emphasis should be on long term stability.