Acid etching is a process that uses a strong acid to cut into another substance. It is used for both industrial and artistic purposes. For example, etching can be used to prepare flooring like cement for painting or refinishing, while artists use it to create detailed pictures on metal or glass.
In acid etching of concrete, chemicals like muriatic acid, phosphoric acid, or sulfamic acid are used to prepare flooring to accept epoxy paint. Floors must be clean, and users must proceed with extreme caution as the acids used can be very dangerous. The acid is prepared as a liquid solution that is brushed over the floors, and then cleaned off before paint is applied. This process is typically used by home owners to finish and protect flooring in garages, basements and shops in the home.
In artistic metal acid etching, a metal sheet is covered in a waxy substance called a ground. The artist uses precision tools to create designs in the wax. The sheet is then dipped into an acid bath, which etches, or eats into, the areas where the metal has been left exposed. Once the acid has etched the exposed metal to the desired depth, it is removed from the bath and the ground is cleaned off. The etching can then be used with ink to produce identical paper images in much the way that a printing press does.
A similar acid etching process can create glass etchings as well. A "resist," usually made of wax, or a similar sticky substance, is placed on the glass where the natural color is to remain. The glass is then dipped into a hydrofluoric acid bath, after which the resist is removed and the etched image will be visible. This process is extremely dangerous, however, so the average home craft enthusiast will often choose a much safer etching cream for small home projects on glass. A stencil is placed on the glass and etching cream is wiped over the stencil leaving behind a cloudy pattern. Although they are sometimes confused for acid etchers, these etching creams do not eat into the glass for a permanent etch like hydrofluoric acid does.
Photo acid etching is an offshoot of metal etching. Instead of using a ground, an image is printed onto special paper to produce a photo resist that is then placed on the metal. The sheet is then exposed to light to place the image onto the metal. The sheet is then dipped into the acid bath and the image is etched into the metal. A light etch can produce a plate similar to a standard metal etching, while a deeper etch can make it possible to literally punch the image out of the metal for metal models, or various types of decorations.