Make sure you wear latex gloves when working with etching cream; a long sleeve shirt and eye protection are also a good idea. Make sure the area you are working in is well-ventilated and the work surface is covered. The etching cream is an acid and it will etch anything it comes in contact with.
Clean your glass using window cleaner. Make sure it is dry and free of all dust and lint.
Cut a piece of contact paper at least a few inches larger than your pattern.
Place the contact paper on your glass where you want the etching to be; smooth out all air bubbles.
Place the carbon paper over the contact paper and then place the pattern over the carbon paper (secure these with a few, small pieces of masking tape if you like).
Trace your pattern onto the contact paper. Once done, remove the pattern and carbon paper.
Using a sharp utility knife cut all the details out of the contact paper. Remove pieces of the contact paper so only the sections of the glass that you want etched are exposed.
Make sure that all of the edges of the remaining pieces of contact paper are stuck tightly to the glass.
Put on the latex gloves. Use a foam brush to spread a thick layer of etching cream onto the exposed sections of your design (you can also use a paper towel). Be generous with the etching cream; if it is applied to thinly, your pattern could look uneven or streaked!
Set your glass in a safe spot and wait the amount of time required for the brand of etching cream you are using (this can vary, usually from 5 to 15 minutes).
After the prescribed amount of time, remove the etching cream usually by running water over it. Again, read the specific instructions for the brand of etching cream you purchased.
Once the cream is washed off you can remove the contact paper to reveal your design. Wash your glass and you are done!