Adam G Cowan's Ghost Cube

Ghost Cube 

The ghost cube was invented by Adam G. Cowan in 2008. Many variants are available.

There is a number of different variants of this puzzle available but I liked the look of the one below and decided this was the one for me. This is a fiendish variant on the Rubik's cube and the one I have found the most difficult to solve with the standard internal, 3x3x3 mechanism. Whoever came up with this has a wicked mind. It is an evil puzzle and not for the faint-hearted.

Each piece of the puzzle has a unique shape therefore to solve the puzzle, each must be put in its one correct position with the correct orientation. While all the pieces are different, some only have subtle differences, therefore, it is not always immediately obvious where they go. This is not a puzzle to tackle if you are not 100% with your algorithms! The frame of reference of a solved side is much less clear than on a coloured cube. It is all too easy to get confused and get lost mid-solve.

The picture below is of a solved ghost cube but the middle layer is rotated such that it has complete freedom of movement like on a normal cube.

Turning the middle layer like this, creates upper and lower layers be the default. It is important to be able to recognise them, as such, during a solve.

This is what it looks like when the puzzle is scrambled. The integrity of the cube shape is quickly destroyed.

Theoretically, anyone who can solve a standard Rubik's cube can solve this one too. In practice, it is not quite that simple. The first time I picked this up, it took me six hours to solve it!

It is a fun a challenging puzzle. The variant I own has never popped. Cornering is not great I sometimes find myself unable to execute a turn, necessitating re-aligning the puzzle. A slip is all too possible creating the risk of a false turn and losing track of what you are doing. Of course, one might view this as adding to the challenge.

Solving the Ghost Cube

The method I used to solve the cube is described below. Unlike on a standard cube, there are no, obviously,  colours to act as a reference.
Before attempting a solve, I studied the puzzle carefully. I worked out which pieces behave as centres. From those points of reference, it becomes clear which pieces behave as edges and which as corners. A "side" then is a piece that behaves as a centre and the corresponding eight pieces, "edges" and "corners", surrounding it. This becomes a layer. See the picture below to show a rotated "side".

Step 1 - Solve a Layer

First, I solved a "side", or layer, as described above.  Care needs to be taken to ensure that the correct pieces are used and that they line up correctly and squarely. This is especially true of the triangular "corners"; they are easy to get mixed up.
Due to how the cube works there are only two choices of a layer to solve at this point. It is important to be able to recognise their "centres".

Step 2 - Solve the Opposite Side

In some ways, this step is slightly easier because there are fewer choices of pieces. Though solving it is still far from trivial. I do the "corners" first followed by the "edges". However, before doing the corners I solve the two ridged "edge" piece to make it easier to visualise where the corners go.

It is possible to encounter a parity odd case at this step but this is easily solved by rotating this layer's centre and one on the E-layer by a quarter turn.

The top and bottom are now solved just leaving the middle layer. This is where it gets interesting...

Step 3 - Solve the Middle Layer's Edges

I found this to be very tricky. Before solving the "edges" it is necessary to work out where the "centres" go and then solve the "edges" relative to them. This is further complicated by the fact that the middle layer must be rotated away out of synchronicity with the upper and bottom layers. This makes this stage very confusing and significantly more difficult. I found it easier to orientate one of the "centres", at this point, so that I could use this as a reference point by turning the middle layer to the solved position and then check the positions of the "edges".

Step 4 - Orientate the Middle Layer's Centres

So, after solving the middle layer's "edges", it is time to orientate the "centres". This is not something to learn on a ghost cube but it can be mastered on a super cube (a normal cube with pictures or numbers on the stickers) or, the Fisher or Wheel cubes.

If it has been done correctly, turning the middle layer to the solved position will result in a perfectly square cube.

Update

I have since got another ghost cube, this one with nebulae printed on the sides. This puzzle is easier to solve than the one above.