Although it's not necessary to make an Amber Cube for this mission, it's almost a shame not to. The project is pretty dang simple, looks great on the table, and will turn heads.
First off, run out and grab some sort of base to serve as a dais for the cube. A cheap, pre-made, routed wooden base is ideal (they're available at most craft stores). Add some arcane decoration with plasticard or – like the example here – a few metal bits from the Warhammer Siege range. Glue the decoration onto the base and paint it up. For the base pictured above, we used a series of grey spray paints over a black undercoat followed by a quick bit of drybrushing. With the base all set, it's time for the cube.
Locate a sports card store or hit the internet and look for a two-part baseball holder made of clear plastic. Normally these holders are used for signed baseballs and memorabilia, but we will use it to house a Daemon instead! With 3M Safe Release Masking Tape (the good stuff), mask off the outer planes of the cube so you leave the inside and thin edges of the cube exposed. The cube is now ready to be painted and you have two methods to choose from: airbrush or spray paint. If you want the cube to maintain its translucency like our example, find some Createx Transparent Airbrush Colours. Craft and art stores like AC Moore or Michael's will have this special type of airbrush paint. Mix up a colour that pleases you (here, we mixed Createx Orange and Light Brown), mix it with rubbing alcohol and lightly airbrush the inner planes of the cube. If you do not have an airbrush, just pick a spray paint colour and spray away – though this method will leave the cube opaque as opposed to translucent. Set the cube aside to dry (far away from dust and static grass!)
While the cube dries, tear off a hunk of steel wool and shape it into a teardrop. Paint this shape a dark colour like black or deep red to represent the swirling essence of the trapped daemon. Alternately you could glue a primed model inside of the cube to make for a shadowy figure within. Place the smoky shape or model within the confines of the cube and reassemble it. All that's left to do is glue the cube to the base. Avoid super glue as the "misting" effect common with this substance will mess up your cube. Instead, use Liquid Nails, another suitable adhesive, or just leave the cube loose on top of the base. Feel free to "buff" the cube with a clean paper towel for maximum mirrored shine!

Armies of the Warhammer 40,000 Universe
Black Templars
Dark Angels Orks
Catachans
Dark Eldar Space Marines
Chapter Approved
Eldar Tau
Chaos Space Marines Imperial Guard Tyranids
Daemonhunters Necrons Witch Hunters