User blog comment:Yatanogarasu/What Did Blackbeard Do to Get the Gura Gura no Mi?/@comment-3387274-20120816074103

Well, I was hoping some one would bring this up. I thought it through a few months back;

1) it is noted that Logia powers cannot transorm when exposed to something that would bind their element together or cause it to disolve or evaporate; Enel and Croc prove this.

2) Shine a torch into a shadow, and there is no shadow. Darkness dissapears in light. Therefore BB's weakness is almost certainly light, and not even Kizaru grade lasers; even ordinary daylight, even moonlight, starlight, anything, would be enough to limit his power; if he is vissible, that is because he is being exposed to at least some light. This is why BB cannot transform.

3) a completely black cloth, if it was entirely undamaged, and was thick enough, would block out all light. provided it rested completely on the ground so he was fully concealed, that would allow him to transform.

At this point, I think you can guess where I'm going. it must also be said that if the DF is involved, which is strongly implied to be the case, he would not need to conceal his method, since nobody else could use it. The cloth must serve some other purpose.

with that out the way, let's continue:

The properties of the darknessis gravity