The Vari-Etch is a powerful etching acid for your glass and thus only needs about 4-5 minutes to properly etch your glass. Many customers will decide to keep their glass submerged in the Vari-Etch for longer periods.
While there is nothing wrong with that, it will etch away more glass and you'll have small bits of glass that will trail down your glass or float across it and leave a streaked surface on the final etch. If you decide to leave your piece in the bath for more than 4 to 5 minutes for a deeper etch, then periodically remove and wash down the piece to remove the small bits of glass that cause these streaks and then re-submerge in the bath.
If you are trying to etch plate glass, then please be aware that most plate glass is float glass and Vari-Etch will have a hard time etching the tin side of the glass. You will need to sandblast the surface to remove the tin before trying to etch float glass.
You also need to be sure that your surfaces are properly cleaned and that all dirt, oils, and surfactants are removed from the glass before you try to etch. Anything on the surface of the glass will act as a mask again the etching liquid and prevent a smooth etch on the surface.
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