Monitoring system based on etching of metals

A process to monitor the status of medical products, food, or biological waste which comprises placing an indicating system comprising:

• a zero-valent metal or metal alloy indicator layer;
• a metal oxide layer;
• a layer of an activator or a precursor of said activator on a packaging of said medical products, food, or biological waste;
• and
• the system is capable of providing an induction period.

A process to monitor a limited time consumer use for items that have been opened or in use and should be used within a certain period comprising:

• placing an indicating system comprising a zero-valent opaque metal, metal alloy indicator layer, or a metal oxide layer and a layer of an activator or a precursor of said activator, near an item to be monitored, wherein the item is selected from the group consisting of drinks, food items, health, personal and family care products
• wherein when said indicator becomes transparent said certain period has expired;
• and
• the system is capable of providing an induction period.

A process to make an indicating system comprising a zero-valent metal, metal alloy indicator layer, or a metal oxide layer and a layer of an activator or a precursor of said activator comprising:

• coating said layer of activator or precursor of said activator on said metal, metal alloy or metal oxide indicator layer wherein said metal, metal alloy or metal oxide indicator is on a support;
• coating onto said support at least one additional layer selected from the group consisting of a permeable layer, a wedge shaped permeable layer, a barrier layer, a reactive, destroyable or degradable barrier layer, an expiration indicating layer, a tamper indicating layer, an activation indicating layer, a message or image creating layer, separating layer, removable layer, a disappearing layer, activatable layer, a microencapsulated layer and a thermally printable layer;
• and
• the system is capable of providing an induction period.

The indicating system comprising:

• At least one substrate;
• an indicator layer comprising a zero-valent opaque metal or metal alloy;
• a layer of metal oxide;
• a layer of activator or a precursor of said activator wherein said activator or said precursor of said activator in a polymeric matrix/binder renders said indicator layer transparent upon reaction;
• wherein
• the system is capable of providing an induction period.

A process of creating induction period in an indicating system which comprises

• placing an indicating layer on a substrate;
• exposing the indicating layer to an activator;
• and
• allowing the activator to destroy the indicating layer;
• wherein the indicating layer is not destroyed immediately, thereby creating an induction period.