Etching Glass
From GlassHaven Knowledge Base
Glass Etching
Surface texture can be developed on glass surfaces by a couple of different methods. Chemical etching leaves a relatively smooth-appearing surface and is good for shallow surface texture. This process works well with soft glass but is ineffective for borosilicate glasses. Media blasting (sandblasting) is a more aggressive method which can be used to develop a deeper relief surface on all kinds of glass. Textures may also be varied from rough to very fine using this method. Don’t etch glass in your kitchen.
Chemical Etching
Chemical etching uses an acid to dissolve a thin layer of glass, leaving behind a microscopically roughened surface. This surface will have a ‘matte’ finish. This type of surface will hold paints or other materials which would flake off of a high gloss surface.
A ‘resist’ may be applied to areas of the surface that you want to remain glossy. This material should be non-water soluble, such as nail polish or a polymerizing adhesive, and should be completely dry before chemical etching. Deep chemical etching may be a slow process and may extend under resist materials, softening or obscuring details. Shallow etching is advised. The resist may be removed after the etching process by solvent or peeling.
Glass may be immersed in an etching solution for varying lengths of time, but usually 5-15 minutes will generate a smooth surface. Stirring or agitating the solution will promote even reaction and a more consistent surface texture. Different colors of glass may have stronger or weaker reactions to the etching solution depending on the colorant components, so some experimentation with time and agitation may be required in order to achieve consistent results.
After the etching process the glass must be cleaned to remove any residual etching compound. Rinse the glass thoroughly in cool water, then place it in a solution of baking soda and water (1-2 tbsp/8 oz) for 10-20 minutes to neutralize any acid that may remain on the surface. Agitate the solution to insure that all areas, including mandrel holes, have come into contact with the neutralizing solution. Wash again in cool water.
Safety
Glass etching solutions contain hydrofluoric acid (HF). This is an extremely dangerous material and should always be used with caution (http://en.wikipedia.org/wiki/Hydrofluoric_acid) . Wear nitrile gloves at all times when working with etching solutions and use them under ventilation. HF penetrates the skin without leaving a burn, but will attack the calcium in underlying bone causing serious and painful injuries. Commercially available etching solutions usually contain ammonium fluoride (http://en.wikipedia.org/wiki/Ammonium_fluoride), which releases low concentrations of HF to do the work on your glass. Wear skin and eye protection when using these materials. Use plastic containers dedicated to etching for etching and washing processes. Do not use etching creams or solutions in food preparation areas. Do not heat etching solutions (microwave, stove top, etc.) as this will release highly toxic HF gas. Do not etch glass in your kitchen.
Sandblasting
Sandblasting, also known as media blasting, is a general term that refers to the use of particle impaction to remove surface layers from a material by an abrasion process. The abrasive particles are typically carried by a stream of compressed air (or other gas) directed by a nozzle. Media blasting finds applications in cleaning, polishing and etching processes. For glass materials media blasting is most often used to replace the typically high gloss surface a frosted texture. Small scale media blasting is usually done in a dedicated cabinet. These cabinets typically are connected to a dust collector to retain the dust generated from blasting by use of while allowing operator access though gloved ports. Eye and airway protection (see below) should be employed whenever a media blasting cabinet is opened.
Safety
Dust in your airways and lungs is a bad thing, especially glass dust (bad enough by itself) which may also contain small amounts of heavy metals. Sandblasting with sand was found to contribute to an inflammatory lung disease known as silicosis, hence the need for dust protection. Surface blasting with any media requires proper safety precautions, including airway protection and proper ventilation. Media blasting glass will generate very fine particulates (media particles and glass dust) and should be done under a hood with air filtration and exhaust. Personal airway protection (respirator) and gloves should always be employed in addition to ventilation. Eye protection, safety glasses or goggles, should always be used when media blasting. Don’t media blast in your kitchen or other in living areas of your home.
Media
There are a few media choices for blasting glass. Traditional ‘sand’, or silicon dioxide, can be used with varying results. Harder glasses will be more resistant to sand impaction. Aluminum oxide (Alumina) is probably the most commonly medium used by the hobbyist. It is available in a range of particle sizes, or ‘grits’, with larger grit sizes yielding rougher texture on a surface. Starting with large grits followed by smaller sizes will refine the surface texture. Aluminum oxide is also available in several purity grades, up to 99.5%. Silicon carbide is a ceramic material and the most aggressive medium typically used for media blasting glass. This material may be used to cut deeply into the glass surface very quickly. It is also available in a range of grit sizes.
Media Blasting
Particles of abrasive medium are carried at high velocity by the compressed air stream as it leaves the ‘gun’ nozzle. These particles strike the glass and break small chips of glass loose from the surface. Higher operating pressure and large particle size will remove larger pieces of glass resulting in a more coarse texture. This texture is composed of pits where glass has been removed and, usually, small cracks. Smaller grit sizes will reduce the pit size and the depth of cracking and generates a smoother surface. The textures generated by media blasting will retain small amounts of pigmented materials (paint, ink, etc.) applied to these surfaces, making this type of surface preparation very effective for application of a variety of decorative materials.
Resist materials are available for media blasting which will allow the retention of glossy areas on surfaces. Resists will allow for deep etching without ‘creep’ under detail edges. Patterns may be cut from adhesive vinyl or rubber sheets and applied to the glass for detailed etching. Photoresists, resins polymerized by ultraviolet light, may also be used but tend to be complicated and expensive for the casual user.
Tumble Etching
A tumbler of the sort used for lapidary polishing can be used to ‘tumble etch’ glass. This method works well for borosilicate glass beads. The beads can be placed in the tumbler with plastic pellets, silicon carbide polishing compound (800-1000 grit), and enough water to cover. The plastic pellets act as spacers to keep the beads separated. Tumbling takes a few hours. Stop the tumbler and inspect the work occasionally to determine the progress.
Page created by Robert Simmons
