What's the best way to cleanse a pendulum?
For a pendulum, you're probably looking to cleanse it of ALL energies but only the BAD spirits (I might be wrong with this but this is what I know, so if anyone wants to correct me I’ll edit this asap!).
I recently answered an ask on cleansing an area using a cleansing “medicine”, but if you follow the same steps to make the medicine and alter the chant, you could just use it on the pendulum (if you have a metal chain, take care to avoid getting the water on it or it might rust!)
Alternatively, writing a statement of intent on a piece of paper, placing it under the pendulum and leaving the pendulum in moonlight for 1 night can cleanse it. Full or waning moon is best but not a requirement!
Other people cleanse items with Earth energies instead of Lunar or Water energy, although I personally don’t tend to do this due to home life compilations. It requires burying the item (if it won't get ruined) in the ground for 8 hours.
Incense cleansing (running the item through incense smoke - sage is best), visualisation (visualise white energy filling the object, ridding it of impurities) or running water cleansing (hold under running water and know that it washes away the impurities) are also good methods.
Basically, any of the above or any combination of them will thoroughly cleanse a pendulum ready for use! The only difference is that you have to work a statement of intent into ANY of them, to specify you want to preserve the positive/kind spirits (if you believe in spirits). I personally feel the moon cleansing is best for magickal equipment :)