The processes involved are typically as follows. Glass in storage is wetted by condensation, which usually forms due to a drop in temperature. The most common cause of temperature variation is the daily cycle of temperature from day to night. However, similar variations can occur due to transportation as well as storage.
This condensation leaches out alkali ions (sodium and/or potassium) from the glass leading to the formation of an alkaline solution. As the temperature rises throughout the day the liquid evaporates and leaves a more concentrated alkali solution. Eventually, all the liquid evaporates from the surface leaving alkali salts on the glass surface. These are usually in the form of carbonates from the reaction with atmospheric carbon dioxide.
Factors that can affect the severity of this reaction are the humidity and temperature stability of the storage area, the packaging of the pallets and local weather conditions. While there are no set times for storage in any environment before the onset of weathering, this is an effect that normally occurs only after extended periods of storage under adverse conditions. Ideal storage conditions would be dry, well ventilated areas with a relatively constant temperature and low humidity.
From the above discussion, it can be seen that the occurrence of weathering is a complex issue. The mechanism is complex and normally requires many cycles of temperature and condensation to cause visible deterioration of the glass surface. Consequently, the phenomenon is not related directly to chemical durability under normal use, therefore, unless the product being filled is sensitive to alkali (PH) levels, for example eye drop solutions, the presence of weathering is not expected to have any detrimental effect on the filled product.
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