Wembley's QuickFix glue (preferably, not tested with other glues, if other glue is used, it should be transparent, or shouldn't give much yellowing or whitening when dried), Glitters (with glue ones would work better, Option 1 ), Coloured Marker set (Option 2, or Glass Painting Kit ).
INSTRUCTIONS (FOR PHONES WITH COATED PANELS):
1. Spread the QuickFix all over the back panel, excluding the silver rim of the lens. Wait for sometime and watch the coating develop cracks bit by bit.
2. After sometime, when the glue* has dried, you will obtain a nice texture with lots of ridges on the surface. The obtained texture will be different for each and every one, as the cracks will tend to develop randomly. You might notice many bubbles on the surface. If you do, try bursting them before it solidifies and smoothen it.
3. If you're not opting for glitters, then you can start coloring** the pieces randomly, avoiding similar colors side by side. However, in this method, the colors won't be very vibrant, and will be particularly noticeable under bright light only. If you do not like it, you can continue on with the 4th step.
4. Using glitters of different colors, start putting them in the pattern, avoid a thick layer of glitter. Let it dry (for the ones with glue).
5. After the glitters have dried, you will get a rough glittering texture. To avoid glitters from coming off, you may apply another layer of quickfix on top. It will reduce the shine a bit, and will increase gloss texture, but will keep the glitters from falling away.
6. You may opt for overcoating the silver rim around the camera lens (Only if you are using glitters, otherwise, it looks plain bad). Apply a thick layer of glitter over the rim, and overcoat it with QuickFix. Let it dry.
* If some other glue is used, you may or may not get the ridge texture. In that case, you can use a glass painting kits, black ones for borders.
**You may use glass colors for coloring as well, avoiding too thick layers.
Particularly for 5800 Users: Incase your lens cover is broken, you can take out all the fiber glass from the cover, except for the flash glass cover (it won't come out if you try removing the other glass). Buy an OHP sheet (transparent sheets, you can get them from Stationary Shops). Cut it out of the appropriate size, place it, hold with something small like tweezers or pluckers, and apply glue on the edges. Make sure to avoid smearing it in the middle, as it will drastically reduce image quality. After it dries, keep reapplying the glue so as to thicken the edges, and the OHP sheet is left inset.
INSTRUCTIONS (FOR PHONES WITH PLAIN PANELS):
Similar to the phones with coated panels, you can follow similar procedure. You will not obtain any texture on drying of the glue. You can opt for making borders manually use glass painting kits.