A magical core is a material placed magically into the core of the wand running from end to end. This may have a physical form that carries the enchanted essence, but it may also be completely astral. Some wandmakers like to include material articles inside their wands, such as feathers or hair, either concealed in a compartment in the handle or inserted into the hollowed center of the wand’s shaft. Trees that have a pithy center to their branches can be hollowed out with a wire or other tool. Other types of wood can be drilled to create a physical hole.
People have included actual bird feathers, herbs, a lock of their own hair, and drops of their own blood. All of these inclusions can make the wand that much stronger for the user as she feels more closely bonded to the instrument.
Franz Bardon and some mages of the Hermetic Order of the Golden dawn have stipulated the use of magnetized wire as a core. Bardon also suggests the use of metals and other substances combined to make “fluid condensers,” substances that “condense” and concentrate the prana of the wand wielder — that is, the yin and yang “fluids.”
In her Harry Potter books, J. K. Rowling came up with the idea of using the bodily ephemera of mythical beasts as wand cores. Mr. Ollivander, the wandmaker, somehow places unicorn hairs and phoenix feathers into the centers of his wands. When Ron Weasley breaks his wand in Harry Potter and the Prisoner of Azkaban, he can see the unicorn hair exposed. In this fictional world, unicorns and phoenixes are as materially real as ordinary animals, only magical.
For real wizards (as distinct from fantasy ones), unicorns and phoenixes are real just as elves and gods are real — in the higher planes of existence. Their appearing in material form is rare. Creatures and persons on the astral plane or the higher dimensions of being have their consciousness located within those dimensions or worlds. They may have a material existence in some other world, but from our material point of view, such existence is invisible to the material senses. The person in the material realm may see or hear, and even touch and smell mythical beasts with his or her etheric senses. Those born with “the Sight” have these senses awakened without training, but most wizards train their minds to use the etheric senses and to pass between dimensions. The astral dimension, as it is commonly called, is a realm where dreams are true, and as such is the home of the mythical beasts of heraldry and the medieval bestiaries.
Rather than making a physical hole in the wand, I enchant the magical core material into the wand. This is done imaginally, through the power of the astral consciousness of the maker. A trip to the astral plane may yield a unicorn hair, a phoenix feather, and even a dragon scale that can be thinned down to the size required to act as the filament of spirit in the center of a wand. The wand is already animated in the process of enchantment when the dryad spirit of the tree is awakened in the wand, but I find that the addition of something animal into the combination of etheric forces, gives the wand that extra dimension of complexity and character. If the wand also has a stone or crystal, it then manifests the animal, vegetable, and mineral kingdoms.
A gryphon is not a bear, nor is a serpent a phoenix. Mythical animals often combine elements of two or more ordinary animals giving them a composite character. Symbols are the stuff of magic and mythical creatures are precisely that: symbols that are alive and well in the astral dimension of existence.
The feathers or hair of any animal can also be used in this way. An owl, snake, or boar may lend a feather, a slip of skin, or a bristle imaginally to the wandmaker to enchant a wand with their particular power. It is important to understand that I am not talking about the physical insertion of the bodily ephemera of material owls or boars into the material boy of a wand. Rather, the core material is astral and is inserted into the astral body of the wand, through the power of the mind. This is, to my way of thinking, a much more relevant and powerful sort of core material than anything material. Why? Because it is already in the astral dimension, which is the dimension through which magic is affected. A material owl feather serves as a representation of the symbolic, astral existence — that is, those qualities mythically and heraldically afforded to an owl. Which is fine, but it is the astral dimension of the owl feather’s being which holds the imaginal, magical power. It is, in other words, the meaning of the symbol, not it’s actual material existence that is effective.
In the end, it is not the physical wand that the mage uses to direct his will. A wand is only a tool for that purpose and its astral body must accompany the mage to that higher plane in which magic is done. The wand itself is both symbol and tool, for, in the magical arts, symbols are tools.
Source: Use of Core Materials in Wands