Etching windows for privacy is a great way to deflect the prying eyes of neighbours and passersby without sacrificing the flow of natural light. Etching to take a window from see-through to opaque also eliminates the need to cover windows with blinds or curtains that require cleaning periodically, especially in homes with pets and/or children. The traditional active component of etching pastes and solutions is highly toxic hydrofluoric acid, which is so hazardous that it is potentially fatal. It's also hazardous to dispose of it after use. Today, etching pastes that contain no acid are available and present a safe way to achieve the same effect as both hydrofluoric acid and the alternative, heavy machine-based sand blasting technique.
Select the window to etch and open all the doors and windows around it, or remove the window and take it outside for applying the etching paste.
Mask off the window glass from its door or window frame with masking tape so that only the glass is exposed for etching. Place the edge of the masking tape along the outside edge of the glass so that it covers the wood or metal frame. Stick the tape down firmly to create a barrier between the glass and its window frame to prevent any of the etching paste from oozing beneath the edge of the tape and getting on the frame.
Read the etching paste manufacturer's instructions carefully. If any of those instructions differ from or contradict the following steps, follow the manufacturer's instructions.
Put on your protective eyewear and gloves.
Apply a thick line of etching paste onto the edge of the rubber squeegee, then touch the squeegee edge to the top corner of the exposed glass and pull the paste down over the glass. Work quickly to cover the entire glass area with the paste.
Allow the etching paste to sit on the glass for 10 to 15 minutes, then squeegee the paste off the glass and scrape it back into its original container for later reuse.
Wash the last of the paste off the glass with running water from a faucet or garden hose. If holding the window under running water, or using the running water from an outside hose, is not an option, use a damp sponge and gently wipe the last of the etching paste from the window.
Dry the glass with a soft cloth, then slowly peel off the masking tape and throw it away.
If you sponge off the remaining etching past residue at the end of the project, do not reuse the sponge for any other project or household use. Discard the sponge as soon as the paste is completely sponged off.