Identifying a Transfiguration can range from being very simple to being extremely complicated. It all depends on the complexity of the Transfiguration, the skill of the witch or wizard in question, and oftentimes the number of Transfigurations already undergone by the object.

Basic Casting

While identifying previous spells can be done with the simple incantation Priori Incantatem, Transfigurations tend to be harder to identify. The incantation used is Priori Mutatio (pronounced moo-TA-cio). This should be said while moving your wand first diagonally upward, then quickly down in a sweeping motion. The first movement should be made in a wide, sweeping, arc, while the next may be quite sharp.

Assuming the spell is cast correctly, the object in question should emit a pulsating glow. If the object has never been Transfigured, the glow should flare bright white and subside quickly. A Transfigured object will glow various shades of purple. As a very general rule, a darker shade signifies a greater number of past Transfigurations. Conjured objects will glow pure black. However, complexity and other random factors may also affect the color. Therefore, Priori Mutatio is not in itself a sufficient test.

The spell works by reading the amount of magic woven in amongst an object’s particles. Magic leaves its traces in Transfigured objects; as a Transfiguration spell weaves its way through, changing an object’s molecular structure, the magic becomes embedded within the object itself.

Multiple Transfigurations upon the same object build up, adding to existing magical bonds. Conjured objects are difficult to create and maintain precisely for this reason. Without a base of a non-magical object, their molecular structure becomes much harder to control and maintain.

Progressions through Difficulties

The simpler the Transfiguration is, the simpler the task of identifying its original state. Priori Mutatio tells whether or not an object has been Transfigured; Indietro (pronounced in-DI-e-tro) tells what state the object was in immediately before the Transfiguration. The wand movement is the same as the movement for Priori Mutatio; however, it should be smaller and more targeted.

Once Priori Mutatio has been mastered, the only problem with Indietro is casting it rapidly in succession. Going back to the simplest of Transfigurations, a match to a needle, this is easy to identify. On casting of Indietro should create a shadow of the original object, and by casting Priori Mutatio upon this shadow, one learns right away that the match is the original state. However, most Transfigurations are not so simple.

Consider the following case. The original object was a short-sleeved t-shirt. Cold, a wizard Transfigured it to have long sleeves. Later that night, it became an extra blanket when his house’s heater broke down. Now, two days later, the heater is fixed and the wizard wants his short-sleeved t-shirt back. The problem is that the Transfigured blanket looks exactly like all of the rest. (Note: It is actually possible to Untransfigure an object without knowing its original state or subsequent Transformations. However, it is an immensely difficult piece of magic, to be discussed in detail later.)

The first step would be to cast Priori Mutatio over each blanket in question until one glowed purple. Then he would cast Indietro, creating a shadow of a long sleeved shirt. The wizard now has a span of about 15 seconds before the shadow dissolves in which to cast Priori Mutatio again. The purple glow would show that there was still an earlier state. This he would continue until the only glow on the shadow was white. From here, the knowledge would aide him in taking steps to Untransfigure the object in question.

It is best to practice both Priori Mutatio and Indietro on simple, one-step Transfigured objects at first. A complete mastery is not only helpful, but necessary, to identify the original state of many-times changed and Transformed objects. A strong Indietro buys a witch or wizard more time to cast Priori Mutatio and re-cast Indietro. Missing the time will result in the shadow of the object dissolving. Such a mistake, even if made on the very last stage of identification, results in losing all results. This forces a witch or wizard to start over completely from scratch.

Exceptions

Priori Mutatio and Indietro do not work on Human Transfigurations. It does not matter whether the spell in question was a simple colour change, partial Transformation, Animagus Transformation, Metamorphagus Transformation, etc. Because witches and wizards already have magic ingrained in and about them, Indietro is useless and Priori Mutatio can backfire. Identifying these Transfigurations is inherently difficult and requires a subtler means of detection, different in each situation.

Applications

Untransfiguring an object without knowing its original state is one of the most difficult aspects of Transfigurations, and is not taught until your sixth or seventh year. To Untransfigure a known object is rather simpler. The method discussed above can give a witch or wizard a clear, organized picture of the object’s paths through Transfigurations.

As discussed above, subsequent Transfigurations embed more and more magic within an object, inadvertently making it less stable. With less substantial particle mass, the object has less holding it together and, therefore, is more likely to collapse in on itself, Vanish spontaneously, or react in another shape or form that can be potentially dangerous. By identifying past Transfigurations, a witch or wizard also creates a fairly accurate estimate of how many more Transfigurations the object can take before it becomes dangerous.

As Transfigurations are vital to aid in disguises, these spells are particularly useful during times of war. As recently as the second war against He-Who-Must-Not-Be-Named, quick-casting witches and wizards tested items for instability before Transfiguring them to meet their uses.

Skill

A common mistake made by young witches and wizards as they first learn Transfiguration is overshooting. The focus involved forces them to expend all of their energy on the simplest of Transformations. The problem with this is that the object in question can now only be safely Transfigured a very few times. This is why teachers are recommended to supply enough practise objects, at least at first, in order to give each student his/her own without reissuing.

As learning progresses, a certain subtlety should develop naturally. A witch or wizard will come to a point where he or she expends only absolutely necessary effort to accomplish a Transfiguration, or with any other spell. The same object (again the complexity of the Transfigurations must be factored in) is now usually safe to work on about ten to fifteen times without reasonably expecting any problems.

Transfigurations by skilled witches and wizards are, therefore, much harder to discover and read. Their own skill carefully weaves in only the bare necessity of magic to accomplish their goal.

Priori Mutatio should be cast several times with the wand pointing at different aspects of the object if one suspects such a case. The purple glow may be faint enough or short enough to seem almost un-Transfigured. By aiming the wand at different points on the object, a person is more likely to find the place where the Transfiguration was cast. In other words, they will have an easier job of finding where the magic is the strongest or most present.

Still, it is important to note that it has been proven thus far impossible to completely hide the evidence of a Transfiguration. While a powerful caster can mask their work to the best of their ability, a witch or wizard of similar or greater talent or skill will be able to identify the Transfigurations they have made.