We can stop here, but we are still not pleased with the cube's look, so that's what we'll do more:
- arrange the front corner with some illuminations touch
- putting some irregularities the outer edges of the cube, to give it more realistic look
- arrange a nice background
So, create a new layer, name it 'corner' draw a selection around left edge of the ice cube front corner, set a feather about 10 value, and fill the selection with blue (#3287d7), as seen in the picture below; select again dodge tool (range:highlights, exposure: 50-80%) and draw the reflection areas. Using different exposures values you can emulate spot of lights near diffuse light. The images bellow shows this:
Tweak, until you feel that you've got the best realistic appeareance, finally remove selections and with a soft brush eraser tool remove the dark blue, just let some around the lighted zone to emphasis the area. Take care at the blending 'corner' layer with the background. Do the same with for right edge of the corner. Or simply just recycle the layer already made, duplicate it, rotate in position and tweak a little.
You may use liquify filter to arrange pixels, layer mask for better blending, brushes, whatever you think will do.
This is my result:
And finally, with a soft brush eraser tool (master diameter:5px) delete some irreguralities around the cube as no real ice cube has perfect line edges. Increase the contrast a little bit, and draw the background with the shadow (remember the light source is on upper left corner !) and some reflections at the base of the cube.
The FINAL result: