A mirror is one of the most versatile tools in a working practitioner's kit, precisely because it does several jobs at once. It can amplify a working, reflect or deflect energy sent your way, act as a surface for divination, help manifest something you're calling in, or serve as a portal between spaces. Understanding which job a mirror is doing in a given working is most of what mirror magic actually is.

There's an old saying that whatever you say to yourself in the mirror is what gets reflected back onto you. This is part of why positive affirmations are so often practised in front of a mirror, speaking or writing something kind and true directly at your own reflection lets it land in a way a passing thought doesn't. A simple version of this is writing a single affirming line on a sticky note and pressing it to the corner of your bathroom mirror, so it's the first thing reflected back at you each morning.
This same principle is why some cultures treat certain mirror placements as taboo, a mirror facing your bed, or two mirrors facing each other, are both thought to trap and endlessly repeat whatever energy passes between them while you sleep or move through the room.

Covering mirrors after a death is a genuinely widespread custom, appearing independently in Jewish shiva practice, Victorian mourning tradition and several other cultures besides. The specific reasoning varies. In Jewish tradition it's largely about turning attention away from vanity and appearance during a period meant for grief and remembrance. In Victorian England, the concern was closer to folklore, that the soul of the person who had died might become confused or caught in its own reflection before burial. Whatever the exact belief, the mirror is treated the same way across all of them, as something that needs to be closed off while death is present in the home.

A mirror is said to hold every reflection that's ever crossed it, every person, and along with them every emotion, memory and bit of energy that person carried while they stood looking into it. This is part of why buying a secondhand mirror, or moving into a home that already has mirrors installed, whether in a bathroom, hallway or dining room, calls for a proper cleanse before you start using it, the mirror is arriving with someone else's history already inside it.

Some practitioners hold that mirrors around the world are connected to one another, and that this connection can be used to reach other dimensions, functioning as a kind of portal. This belief sits behind a lot of scrying and mirror gazing practice, the idea that you're not just looking at glass, you're looking through a doorway.

Positioning every mirror in a room to face you, and to face each other, is a common way to amplify a spell. A single mirror facing you roughly doubles the working, as though you've performed it twice. Two or three mirrors angled to reflect each other and you at once multiplies that far further, since each reflection is itself being reflected again, and again, essentially without end.

The reverse is also true. Turning mirrors away from you, and standing behind them rather than in front, can deflect energy and make what you're sending out harder for other practitioners to see, or harder for someone attempting to divine your intentions to pick up on.

The instinct to avoid breaking a mirror is a strong one, but there's an exception worth knowing. If a home has persistent bad energy that no amount of cleansing seems to shift, breaking a mirror with clear intent can be used to break a cycle. Since a mirror holds energy and memory the way a photograph does, breaking it is a way of breaking a return, stopping whatever's been looping back through it from continuing to do so.

Any mirror you bring into your space, whether bought new, secondhand or already installed in a home you've just moved into, is worth cleansing before use. Smoke it out with a cleansing herb, then follow with a Florida water wash, to clear whatever energy, memory or emotion the previous owner or tenant left behind in it.

A working for someone who has caused genuine harm, intended to make them see and feel the weight of what they've done.