Celtic Masks & other Tribal masks: From the beginning of recorded history, masks have been worn for many reason and by all ancient cultures. The ancient Celtic and Viking peoples used tribal masks as a powerful mediator between the worlds, to frighten away spirits who might be angry, or to represent a Nature spirit - God. I do know that the Vikings used masks and helmets to scare their enemy.
Even the origins of scary Halloween masks go back to the old Celtic festival of Samhuinn (Scottish spelling). These Celtic masks were used to blend in with the dead who were believed to be able to cross over during this time of year because this is the time when the Ovates would do their rituals to help the recently deceased cross over, hence the veil was thinnest. Some of these spirits might have held a grudge or were kind of scary so they would use turnips (pumpkins in North America) and Celtic masks to frighten them away from themselves and their homes. One theory is that the people wore these costumes and Celtic masks to mimic the evil spirits and gain their goodwill and not damage crops or their things.
Owning and Storing a mask: When using a tribal mask in ritual, always remember that the Celtic mask should never be taken lightly. If you are going to learn to use a Celtic mask, you must remember to revere it as a sacred object. Wrap it in a sacred cloth and store it in a respected place. When the Celtic mask is used a lot, it will become a living being with its own power. By putting his own self inside and allowing his body to be shared by the spirit the animal mask represents, the Shaman becomes that spirit. Celtic and Viking masks and often their form and function were passed down through clans, families, or from individual to individual. When a new owner receives the gift, it is usually spiritually reactivated or aesthetically restored by polishing, repainting and redecorating, without destroying the basic form and symbolism. In many instances, however, the mask is used only for one ceremony or occasion and then is discarded or destroyed, sometimes by burning.