Hold under running water (a stream or a tap)
Lay item outside (in a safe place) in the moonlight
Lay item outside (in a safe place) in the sunlight
Either of the above two can also be done by placing the item on a windowsill
Sprinkling with salt
If it feels like it needs a really good cleanse then cover completely in salt and leave for a few hours
Smudge with incense
Smudge with burning sage or sweetgrass
Sprinkle with a cleansing herb like sage and leave for a few hours
Visualise the item being cleansed by a bright, white light
Ring a bell over the item, using the vibrations to cleanse it
Sprinkle with blessed water
Sprinkle with salt water
Bury the item in soil (but remember where you buried it!)
Please be careful, make sure the particular crystal or magical tool is not porous and that it won't be damaged by water or salt.
All of the above can be worked into a ritual if you choose to, or you could say a few blessing words over the item as you are cleansing it.
Really the choice is yours, go with what feels right for you.
Tansy
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Source: http://magic-and-spells.blogspot.com