Have you ever seen an old piece of silver? If it’s just been left out, the silver is probably not very silvery in color anymore. Fancy silverware has to be regularly polished in order to remain shiny. If it stays shiny without being polished, it’s probably not pure silver.
Pure silver exposed to air will begin to turn a dark gray or blackish color. When this happens, the silver is referred to as tarnished. Silver tarnish is caused when the silver reacts with sulfur in the air and forms silver sulfide.
In regards to colloidal silver, exposure to air can cause the same reaction that causes silver tarnish. If your colloidal silver is left open to the air, it will begin to darken just like pieces of silver. Colloidal silver that has been left exposed to air will become ineffective and unsafe to use. If you colloidal silver is gray or black, it should be disposed of immediately.
As well, exposure to sunlight and electronics will cause the suspended silver to be ruined. Sunlight can quickly oxidize the colloidal silver. The magnetic field of electronics and appliances can kill the electrical charge of the silver.
Colloidal silver should be stored in an air tight, dark colored glass bottle away from sunlight and electronics. Reduced exposure to air and light will help prevent unsafe compounds from forming. Keeping it away from electronics will preserve the silver charge for longer.
In general, the shelf life of high quality colloidal silver should be limited to no more than three months to guarantee maximum effectiveness. Even with proper storage, the older the batch gets, the less effective it becomes. Producing fresh colloidal silver in smaller quantities is usually the best practice to ensure you’re using the best colloidal silver possible.