Engraving an image onto a glass mirror is much simpler than you might think. It just takes patience, a well laid out design and a really steady hand.
Step 1: Material / Tools
It may be difficult to find a mirror exactly the size you need for your project, so be prepared to cut glass if necessary. I try to find an old mirror which is thicker and definitely doesn't have any scratches that would ruin your final design.
Glass cutting tools
Dremel tool with accessories
Wood for frame, unless your mirror already has a frame
Pencil / Eraser
Respirator / Dust Mask
Step 2: Design Layout
Clean your glass mirror and inspect it for scratches. If needed, cut your glass down to the proper size.
If no scratches are present, cover entire mirror with masking tape to prevent unnecessary scratches during this process. If there are scratches present, try to incorporate them into your design or rotate your design to cover the scratches.
Begin drawing your design directly onto the masking tape with a pencil, in case you make a mistake it can be erased. Once you are happy with the design, trace over it with a marker. This will prevent your design from being erased from your hand movements over the glass during the engraving step.
Decide which areas you want engraved and which you want left alone. If there are any large areas to engrave, use a sharp knife to trace around the area and remove the masking tape. It will be easier to engrave the larger areas without the tape present.
Step 3: Engrave
While wearing a respirator or dust mask, use a Dremel tool, or something similar, with a metal bit to cut through the masking tape and into the glass. It would be a good idea to use a scrap piece of glass to practice on and try out different Dremel bits to find the ones you will be comfortable using.
Trace your design and engrave the glass to your liking, being sure not to cut too deep into the glass. The idea here is to scratch the surface and remove the top layer. Looking at the mirror from different angles will enable you to get all of the glass etched, especially on larger areas.
Once you have finished engraving, make your wooden frame. If you already have a frame, you can remove the masking tape to reveal your engraved mirror. Clean it once more and put it in the frame.
Hang it on a wall and step back to admire your work.
Step 4: Branch Out
Now you have the basic technique down, go make some more. You are only limited by your imagination as to what you can make. This process works well on clear glass too.
Always remember though, glass is sharp and can cut you, so be careful while handling and definitely wear breathing protection while engraving to protect your lungs from the small glass fragments.