Follow the steps below to achive the effect.
1: Get a brushed metal base ready. See the tutorial linked above for details.
2: Select the rectangle tool. Make sure the shape layers option is selected in the options window (this window usually appears just below the main menu). Draw a square in the middle of your canvas.
3: Select the rectangle if with the path selection tool if not already selected. Select Edit/ Transform Path/ Rotate and rotate the square by 45Ëš. You can hold shift while rotating to snap to 45Ëš exactly.
4: Now choose Edit/ Transform Path/ Scale and make the diamond narrower by clicking and holding one of the little boxes while moving it. You can also scale the object smaller if necessary by moving one of the corner boxes.
5: Rotate it back to make it stand on 45Ëš.
6: Select the object with the path selection tool and just press Apple-C (Cmd-C) and Apple-V to make a copy of the object. You can move the new object that has been pasted over the old one with the selection tool to reveal the copy.
7: Use the Edit/ Transform Path/ Flip Horizontal menu to flip the copy.
8: Make another selection of both diamonds and keep making copies. All the pasted shapes will end up on the very same layer.
9: You can double click the layer icon to change the color of the layer from white to grey.
10: Finally you just need to add a simple Bevel and Emboss layer effect with a high number for the size and Technique selected as Chisel Hard.