Sandblasting Glass: A Window of Opportunity

This Sign Builder Illustrated @SBIMag article describes how to transform a clear piece of glass into a beautiful and elegant artistic creation. With a minimal investment in sandblasting equipment you can generate an additional revenue stream, which can complement your current portfolio of signage products and services.

By Jim Hingst @hingst_jim

Transforming the Plain Pane into Something Not So Plain

Sandblasting is a simple and inexpensive way to transform a clear piece of glass into a beautiful and elegant artistic creation. This is a great way to decorate windows and glass doors, sidelights and decorative booth divider panels. For the enterprising sign maker, a minimal investment in sandblasting equipment can generate an additional revenue stream, which can complement your current portfolio of signage products and services.

Behind the reception desk of  the Athletics-Recreation Center at Valparaiso University are four 48" x 96" glass panels with a 4" border cut in deep with frosted letters. The panels were sandblasted by Calibrated Surfaces of Chesterton, Indiana.

Other than the glass itself, not much more is needed other than some stencil material, the sandblasting equipment and a little creativity on your part. Once you have applied a stencil on the glass, the sandblasting process is relatively simple. Under air pressure, a sandblaster directs a stream of hard abrasive material at the glass, lightly chipping the surface, creating a frosted appearance.  Using overlapping strokes, similar to spray painting, the abrasive etches the glass, putting very tiny chips in its surface.

If the sandblaster is directed in one place for a while, you can actually carve into the glass, creating a three-dimensional sculpted image in its surface. This type of sandblasting is called either sandcarving or staged carving, referring to the technique of using multiple staged maskings.

Preparing the Sandblast Stencil

You don’t need a heavy-duty rubber sandblast mask for etching the surface of glass. Instead you can use a calendered vinyl masking film, such as RTape’s ProGrade™ paint mask. In fact, you can use ProGrade™ for staged glass carving, too.



Chicago Brushmaster Ron Jelinek uses RTape ProGrade paint mask when frosting glass or staged glass carving. 

I have used paint mask film for etching the surface of glass prior to applying animal hide glue, when making glue chipped panels. For these applications ProGrade™ works fine using sandblast medium with a grit size of 100 to 180, at a blast pressure below 40psi.  On the other hand, if you are sand carving at high pressures, then use a sandblast mask, such as Hartco’s S310 or S425.

Here’s the bottom line on selecting sandblast mask material. The type of masking that you should use will depend on a variety of factors, such as type of abrasive, grit size and blast pressure.  In selecting a mask for your needs, it is always best to “Test, Don’t Guess” before going into production.

Cutting the Sandblast Mask

You can cut the stencil using either a plotter or hand cutting the design. Either way is acceptable.  If you are plotter cutting the stencil, after you cut and weed the paint mask, laminate an application tape, such as RTape 4075RLA, to it and apply the stencil over the glass panel. 

If you are hand-cutting the masking, apply the  masking to your glass panel and then transfer your design to the sandblast mask or paint mask.  You can either pounce the design or  you can trace your design onto the masking, using  Saral Transfer Paper. Saral paper is similar to carbon paper, but comes in several different colors.  You can buy it  from Dick Blick (www.dickblick.com). Using a #11 blade in your Xacto® knife cut the mask and weed  those areas, which will be sandblasted and subsequently glue-chipped.

When making glue chipped glass panels, I use RTape ProGrade™ paint mask for etching the surface of the glass before applying the animal hide glue. Prior to the applying the paint mask I coat the glass with asphaltum, which is the black background shown in the photo below. Applying asphaltum is not necessary for simply etching the glass.

Sandblasting Equipment

If you decide to sandblast the glass blank yourself, you will need some basic  equipment.  One common set up includes a blasting cabinet, a pressure blaster and a compressor. This is not the only type of equipment that is available, but is one that is commonly used in sign shops and by those working with glass.   The purpose of the blasting cabinet is to contain the majority of the contamination from the blasting process.  Buy a cabinet with good lighting and a vacuum system for dust collection.  The blaster mixes compressed air with the abrasive medium and blows the abrasive out a nozzle. 

  

Buy a cabinet with good lighting and a vacuum system for dust collection.  Photo courtesy of Eric Elmgren.

Of course, the blaster won’t work without compressed air, so you will need to have a compressor. The size of compressor that you will need will depend on the air requirements of the blaster.  In selecting the compressor, you must consider to two critical factors: pressure (measured in pounds per square foot or psi) and volume (measured in cubic feet per minute or cfm).  In buying a compressor, you should also consider all of the different possible uses for this equipment other than sandblasting, such as spray painting.  For a standard pressure blaster, you will generally need a compressor with an output of at least 5 cubic feet per minute at 40 psi. 

“Don’t skimp on the compressor,” says Cincinnati-based glass artist, Linda Roederer. “It’s really exasperating to wait on air, when you’re working on a larger piece.”

Pressure blasters aren’t the only type of equipment on the market.  A much cheaper option is to buy a siphon blaster. If you buy a siphon blaster, you will need a compressor with higher capacity. What you save in the cost of the blaster, will require a more costly investment in a compressor.   To operate a pressure blaster you typically will need at least a 5 hp compressor; a siphon blaster generally requires a 10 hp compressor with an output of 38cfm @ 80psi.

“If you plan to do any deep carving,” Roederer says, “you really need a pressure blaster.  With a siphon, the best you can do is frost the surface of the glass, which limits what you can do.  Make the investment in the best equipment and pay the extra dollars for a pressure pot and a 10 hp compressor.” 

How you equip you shop will depend on which market segments and applications that you intend to pursue.  For smaller signage, a blast cabinet will suffice.  If you intend to work on large glass projects, a small cabinet won’t do.   “Many of our commercial projects are on a grand scale,” says Cliff Leasure of Calibrated Surfaces in Chesterton, Indiana.  “For these big commercial jobs, we build a makeshift blasting room.” 

When working on projects of a grander scale, Linda Roederer says that blasting cabinets can limit your ability to see what you are doing.  “With a blasting cabinet, you’re working at arms length from your work,” says Roederer.  “I like to get up close to my work.  That way, if I am carving, I can see how deep I’m going, so I don’t break the glass.”  Roederer also says that she likes to work with plenty of light.  She uses a Grainger mercury vapor light with a gasket-sealed housing.

Sandblast Equipment investment:

•           Blasting cabinet with vacuum system………………….$700

•           Pressure blaster…………………………………………..$800

•           Compressor………………………………………………$1500

      Total investment……………………………………………...$3000

Grit Size for Sandblasting.

“For etching the surface of glass, all that you need to do is to lightly blast the surface with a fine grit,” Cliff Leasure says. “100-grit to 180-grit works for me.”

Sandblasting at light pressures using a fine grit abrasive is all you need when etching these glass mugs. Photo courtesy of Ron Jelinek.

What does the grit number mean?  The grit number indicates the size of the abrasive particle.  Just as with sandpaper, as the number or grit size becomes lower, the size of the abrasive particle becomes larger.  As the grit number increases, the size of the abrasive particle decreases.  For example, an abrasive with a grit size of 100 is coarser than a 160-grit abrasive.  Using a coarser grit will produce a coarser finish on the surface of the glass. 

“I use aluminum oxide as my blasting medium, running it off an 80 gallon, 10 hp, 2-stage compressor,” says Roederer.  “I set my pressure at about 40 to 60psi.  For finer work, I usually lower the pressure.” 

Sandblasting Abrasives.

For etching the surface of the glass prior to glue chipping, generally you will use an abrasive with a grit size no smaller than 100.  There are a variety of different abrasives on the market. 

Silica sand is typically much coarser than you will need and is really not suited for glass blasting jobs.  Silica sand has a very other downsides.   The grit size is not very consistent and can vary within a batch.  But more importantly, breathing silica sand dust can cause silicosis, which is a very dangerous and debilitating lung disease. 

Other abrasives include garnet, aluminum oxide and silicon carbide.  Aluminum oxide is a very hard medium and etches glass quickly but can generate a lot of static.  “Sure aluminum oxide has static,” Roederer says, “but that keeps my work exciting.” Electrifying is more like it!

The most expensive abrasive is silicon carbide. It has no silica in its dust, produces very little static and can be recycled over and over.  It is slightly harder than aluminum oxide, so it easily etches glass.

For etching on glass, the two abrasives commonly used are aluminum oxide and silicon carbide. Most people that will sandblast glass use brown aluminum oxide.  Which abrasive you use is a matter of personal preference.  As with any product, each abrasive has its own advantages and disadvantages.

Two types of aluminum oxide are available: brown aluminum oxide and white aluminum oxide. Both aluminum oxides are less abrasive that silicon carbide.  The good news is that because aluminum oxide is a less aggressive abrasive, it is more forgiving, which is polite talk for saying that you will screw up fewer pieces.  The bad news is that because aluminum oxide is a less aggressive abrasive, it will take you longer to etch a piece. In other words, your productivity will be lower.

So why are there two different colors of aluminum oxide?  Brown aluminum oxide is brown, because it is contaminated with iron.  White aluminum oxide is filtered more and does not contain iron.  The brown abrasive is lower cost, but the iron potentially could stain your piece.  The white abrasive causes no staining and the better filtered material is also less dusty. As you might expect, the white aluminum oxide is more expensive. Whether you buy the brown or white, both abrasives will generate static electricity, which can give you a little shock.  The static charge can also make the dust cling to the back of your glass panel, making it difficult to see what you are doing.

While silicon carbide initially costs more that aluminum oxide and other abrasives, the higher cost is offset because it can be reused almost 60 to 100 times. Silicon carbide is a harder abrasive, so it will cut through the glass faster than aluminum oxide. This characteristic will speed up your productivity, but you have less room for error. 

About Sandblast Etching.

Here’s how sandblast etching glass works. Using air pressure, a stream of an abrasive medium is directed at the glass panel.  The tiny particles of abrasive collide with the surface of the panel and chip off little pieces of glass. In its finished form, the panel looks as it has been etched.

Usually glass panels are sandblasted in an enclosed cabinet, which contains the dust produced in blasting, but also collects the spent abrasive at the bottom of the enclosure.  That way the abrasive can be used over and over again, and the dust is expelled from the cabinet by a reclamation system.

In selecting a compressor for your sandblasting equipment, always buy a compressor that exceeds equipment requirements by 25% to 30%. The pressures required to etch glass can vary depending on the type of glass that you are working with. When sandblast etching crystal, which is a softer glass, typical blast pressures range between 20 and 30 psi. 

Float glass, which is what you will use for glue chip projects, is harder and requires higher blast pressures.  According to Linda Roederer, frosting a large piece of glass, can require as much as 80 psi.  She recommends taking your time when blasting so you frost the piece evenly and carefully inspecting the job when you are finished working.  

For etching and carving glass, you will typically need a compressor that can deliver 5 to 10 CFM @ 30 PSI.  Frugality does not pay off in this area.  Picking an underpowered compressor can result in two problems.  The first is that you may not reach the blast pressure required. And the second problem is that you overwork the compressor and it prematurely fails.

After you decide on a compressor, you will also need a good filtering system so the air supplied to the blaster is clean and dry.  Why is that important?  Moisture in your air will cause the dust to clog filters.  This is especially a problem when the weather is humid  or during the rainy season.  Roederer recommends having a moisture separators at the tank and at the pressure pot.  “The moisture separators keep your abrasive dry,” she says, “so you’re not blasting with something that has the consistency of oatmeal.”

If you are considering investing in sandblasting equipment, buy a system with a pressure pot blaster. Both a siphon blaster and a pressure pot blaster need pressurized air to operate. Compared to a pressure pot blaster, the air requirement for a siphon blaster is significantly greater in terms cubic feet per minute. And because the nozzles used with a siphon blaster system have orifices twice a large, they require twice the air pressure.  While you may spend less on siphon blaster, you will need a much larger and much more expensive compressor to run it continuously.

When engraving glass, Chicago Brushmaster Ron Jelinek keeps blasting pressures as low as possible.  Excessive blasting pressures can prematurely wear out the blast hose, nozzle and other system components. Nozzles will eventually wear out.  For this reason, you need to regularly check the size of the orifice.   As the nozzle wears, the orifice enlarges. When the orifice becomes larger, the required volume of air increases.  This puts a greater burden on the compressor.  What’s more, with the larger orifice, more abrasive abrades the stencil mask, which can cause the mask to break down faster. 

“When you’re blasting, whether you are etching the surface or carving, pay attention to what you are doing,” cautions Jelinek.  “If you blast too close, too hard or too long, you can actually burn or melt the stencil and ruin a piece of glass.”    

Sandblast Variables

So what are the variable that you need to concern yourself with when blasting on glass.  These variables include the type of abrasive; the distance between the nozzle and the surface of the glass; the size of the nozzle orifice; the blasting pressure; and the time or duration that you are blasting. Simple, isn’t it.  Of course, if you change one of these variables, you can compensate by changing another variable.  For example, the nozzle typically should be held at a distance of 10” to 12”.   If you are blasting at a close distance to the glass, you should lower the blasting pressure.

“Before working on a project, always test your system and air pressure on scrap glass”, advises Jelinek. “A good place to pick up inexpensive pieces of glass is at a Dollar store or resale shop.”

“Nothing lasts forever,” says Jelinek. “Eventually the threads on the coupler start to wear.  When that happens, air starts leaking through the threads.  As soon as it starts to fail, you need to replace it. If you don’t, the nozzle could shoot off the end of the blaster and shatter the glass.” 

He also says that as the tip of the nozzle wears, the edge of the metal eventually breaks.  Nozzles wear out in stages.  When a nozzle is new and its orifice is small, Jelinek uses them for carving fine detail.  Gradually, the orifice enlarges.  He reserves the nozzles with a wider bore for blasting large areas at high pressure.

Another variable is the angle of the nozzle to the plane of the glass.  Generally, you will want to hold the nozzle at a 90º angle or perpendicular to the surface of the glass.  But not always.  If you are adventurous and try glass carving, you can cut the glass at various angles to create special visual effects.

The Centier glass is 8' square sandcarved on both sides. Letters and firework blasts are raised and clear. Photo courtesy of Calibrated Surfaces of Chesterton, Indiana.

Along with satisfying your creative desires, sandblasting glass panels can generate additional revenue.  While you can certainly sell directly to the downstream customer, you should also consider marketing your services through alliances with construction companies, architects and interior designers.  As part of a larger construction package, glasswork is not a superfluous accessory or adornment. Rather, it can be presented as an indispensable part of the overall design of the interior. By including your products as essential components of the décor, their cost can be amortized over the period of the loan. That way, more ambitious projects are more affordable. According to Leasure, third party sales through designers and construction companies are generally more profitable than dealing directly with clients.  


New! Click here to visit my new blog about heat transfer films

NEW INSTRUCTIONAL VIDEOS.  Five new videos have been added to RTape’s  YouTube channel. The following is a description of the new videos:

Squeegee Technique. Nothing is more basic in vinyl application than the squeegee. But some squeegees work better than others. And there are right ways and wrong ways to use this simple tool. This video clip reviews squeegee selection, squeegee care and squeegee technique. Click here to view the Squeegee Technique video.

Wet Applications. Dry applications are typically recommended for most vinyl applications. For those exceptions to the rule, this instructional video explains the right way to perform a wet application. Click here to view the Wet Applications video.

Introducing AT65. Installing multiple color overlays with a paper application tape is not much easier than driving in the dark without your headlights. For these challenging applications, RTape developed its AT65, the universal high tack film. This video clip explains the features and benefits of this remarkable new film application tape. Click here to view the Introducing AT65 video.

Application of Window Graphics. Installing vinyl graphics on glass can be challenging, because the adhesive aggressively grabs onto this high energy surface. Repositioning graphics on window is generally difficult, if not impossible. This instructional video explains how to dry apply window graphics right the first time. It also describes the necessary steps required for surface preparation. Click here to view the Application of Window Graphics video.

Transferring Frosted Window Graphics Films.  Because frosted window films are highly textured, transferring cut vinyl graphics can be problematic. This video provides direction in selection of the right application tape and how to apply these films quickly, easily and without problems. Click here to view the Transferring Frosted Window Graphics Films video.

About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.

Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer.  Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.

Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for  publications, such as  Signs Canada, SignCraft,  Signs of the Times, Screen Printing, Sign and Digital Graphics and  Sign Builder Illustrated. He also posted more than 325 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.

© 2015 Jim Hingst