SCP Foundation

My last draft ran away from me, so I'm going for something simple with no capacity for power creep

A safe SCP which is a collection of windows. On one side of each window is a plus and on the other side a minus. When something passes through the side with a plus it grows by ~15% and if it goes through the side with a minus it shrinks by the same amount.

The only containment procedures would be keep them shut and stick them in a storage locker.

To avoid the SCP from making every air molecule a mile wide in a day, I'm thinking of restricting the effects to above the molecular. The only detail I'm not sure of is if it should change the density of the objects it effects or add and remove mass.

Is this a good idea, or does it need more than a dumb pun to work?

It seems like you've thought through this idea quite a bit. But once you've figured out what the item does, you've only got half the entry: now you have to figure out what the foundation does with the item.

Have you considered the following (not all have to be answered, but at least some ought to be):
-how it was created
-how it was discovered
-what sort of testing was conducted
-if others have used them in the past, and what happened
-etc.

An entry that just contained "here are these windows, keep them in a box" would be pretty dull. So I guess the really interesting part of the article lies in the Foundation's interactions with the windows.

I personally like the idea of decreasing/increasing density. Is there a hard limit, or does it create a black hole? Can you put a bunch of carbon in and get a diamond? Can you put cake in to make it lighter and fluffier? Is animal testing prohibited? Why would someone create this?