To what extent do charms affect the physical constitution of an object? Does the color charm physically change the color? Does the flame-freezing physically change the way fire works? And of course there's the enlargening charm.

I'd imagine the theory would be more in line with charms, but the effects might overlap with transfiguration. Would the visible casting resemble a transfiguration with the same effect? Is such a transfiguration even possible?

 

Those charms are transfiguration. It's disciplinary overlap, like learning a bit of history in science class.

 

Are they actually though? Would reversing the flame-freezing charm be more like untransfiguration then a finite incantatum?

Also, would transfiguring a large cat be possible? Or must any fully transfigured cat be physically normal?

 

With a charm you apply or alter a trait of an object, but unlike Transfiguration it's still fundamentally the same object.

Personally I think of it like this, if you apply a spell to an object and afterwards when describing it you only have to add or change an adjective then you used a charm, but if you use a transfiguration spell you usually have to outright change the noun as part of of the description.

For example using an enlargement charm on a duck wil just make it a large duck, but using a transfiguration spell could turn the duck into a Rabbit.

 

Per JKR, Transfiguration alters an object's "fundamental nature". She has also said the molecular structure changes. In contrast, Charms do not change an object's fundamental nature, but rather overlay/alter properties.

So if you use a Colour-Changing Charm to turn a red cushion yellow, what you have is a red cushion that appears to be yellow. When the Charm wears off, it will appear red again.

But if you use transfiguration to turn a red cushion yellow, what you have is a yellow cushion. That's what it is now, and you would need to perform a further (un)transfiguration to get a red cushion again.

 

I was actually preparing another post regarding a different aspect of charms, but I think I should bring in some concepts from there over here.

How do you interpret something like the summoning charm, where it moves the object to you, and then releases it from the charm to be subject to physics again? It seems to be a permanent transformation of location, where returning it to its original position would be somewhat like untransfiguration where you manipulate the location but in reverse rather than dispelling the charm.

Although both are permanent, the summoning charm's permanent manipulation of location seems different from something like the permanent sticking charm. If the latter is undone by a wizard, then the thing would just be how it was prior to the charm. With the summoning charm however, the object doesn't automatically return to where it came from after the casting is complete, unless of course it is inherently a permanent charm and it does indeed return to its original location upon the charm being lifted.

 

So do you think you could transfigure an abnormally large duck?

Also, do you think there is a physical difference between a ball that has been charmed red and one that has been transfigured red?

 

You have to keep in mind that transfiguration requires you to actually forma clear mental image of what you are attempting to transfigure something into, so I'd think that it would be almost impossible to truly only change a single aspect of something when using transfiguration, but rather that you are changing it to some degree in it's entirety.

Yes, but assuming you mean turning a small duck into a large duck, I do not believe it would be entirely the same duck anymore, but rather the duck you were focusing mentally to create.

Possibly, when using a charm I think there wouldn't be any change to the ball except for the colour, but I'd think with a transfiguration the ball in it's entirety would change to become now a red ball, which depending on your focus and skill in transfiguration could result in some change in the composition of the ball itself.

A better example would be hair, I assume if you are using a charm to turn a bruenette into blonde, I would assume that the structure of the hair would stay the same and only the colour itself would change, but if you were to use a transfiguration I would think that you are literally turning the hair of the bruenette blonde, which likely would make it thinner as well.