Smart Putty

Minecraft buildings are made from cubes (and slabs and stairs), and as such tend to bristle with sharp edges and right angles. Smart Putty is a special substance intended to smooth out such shapes by molding itself to fit the spot where it is placed.

Mechanics
A putty block is similar to a slab or a fence in that it occupies a 1✕1✕1 meter cube but can have a hit box and visual display smaller than that space. Like fences, but unlike slabs, its appearance and hit box are determined dynamically based on neighboring blocks. Unlike fences, this includes the blocks above and below, and the shape is a sloped geometric plane rather than a series of posts.

Tier One: Simple Putty
Mixing water, clay dust, rubber, and gravel produces an amorphous blob of a beige substance. When placed as a block (or updated), it adapts its shape to match its surroundings. Placing it in the corners of semi-rounded structures produces a smoother appearance. By default, a putty block counts as solid for purposes of shape calculation. A putty block can be re-shaped by right clicking it with a special Trowel tool, which rotates through the possible shapes. This is necessary to permit filling a long corner with a line of wedges, for example.

Tier Two: Custom Putty
Custom Putty has the same shaping properties as Simple Putty, but rather than being limited to a bland beige texture, its appearance is determined by the inclusion of a solid block in its recipe. For example, a blob of Custom Putty made with cobblestone will use a cobblestone texture when placed, and so on with stone, bricks, etc. Where possible, these textures are aligned such that any horizontal lines in the texture are parallel to the horizon line, since the main use case is expected to be the beautification of curved walls.

To encourage occasional use of Simple Putty, the recipe for Customizable Putty is more costly, probably producing about 50% as many blocks per input.

Tier Three: Smart Putty
Smart Putty is a special form of Custom Putty made with redstone dust instead of a solid block. It looks like glowing Simple Putty when in a player's inventory, but when placed as a block (or updated), it blends in by borrowing textures from neighboring blocks. For simplicity, this only works if all such adjacent blocks all have the same texture.

In addition, the shape and texture of a Smart Putty block can be frozen and unfrozen by applying a redstone signal.

Animation
It would be cool if the blobs were animated when changing shape. For example, if I place a solid block next to an existing pyramid, it should stretch out and slowly settle into its new wedge shape. However, this would be significantly more difficult than the basic functionality (which ordinarily amounts to drawing a single flat plane with a single texture), and the main goal would be achieved without it.

Redpower
Redpower mini-blocks are treated as solid if the whole face touching a putty block is filled; otherwise they are treated as non-solid. No mini-wedges or mini-tetrahedrons will be attempted.

Connected Textures
It would be nice if a putty block could count as connected for purposes of drawing textures like planks or iron blocks. However, I have no idea how complex the Connected Textures API is, and again this would be significantly more complex than the basic functionality, so this also is optional.