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What is Sandcarving? 

Sandblasting consists of blowing an abrasive at a surface using compressed air.   Where the abrasive hits glass it roughens, or eventually erodes, the surface of the glass. 

Sandblasting is used on many different materials for many different purposes.  The uses range from cleaning the old paint from the Golden Gate Bridge to carving on gemstones.    When applied to glass, it can create beautiful three-dimensional images that appear to be suspended in mid air.  Two main effects are etching or engraving, which is a surface effect, and sandcarving where the glass is actually carved away.  

Etching glass, or engraving it, refers to a technique where the glass is simply roughened to produce a translucent "white" area on the surface.  This effect is produced by lightly blasting the surface with an abrasive or using hydrofluoric acid.  The results can be a simple monotone design on the surface, or it can be a near-photographic rendering of a scene in shades of black and white. 

Sandcarving is the term often used to describe deep multi-level abrasive etching.  The design is carved in the glass and the edges of the different "stages" can create additional detail with light and shadow.  Edge lighting can produce spectacular effects.  Of course, modern abrasives (Silicon Carbide and Aluminum Oxide) have long since replaced the sand originally used when the process was developed in the late 1800s. 

Whether etching or carving, the process begins when the artist selects a design.   The design is first rendered as a "line drawing", with line weights (thicknessess) carefully selected to reflect the needs of the processes that follow.  The artist will generally use a computer in this process, to ensure that the lines have a consistent quality.  While it is possible to computer generate (i.e., applying various filters in PhotoShop) images for sandcarving glass (just as it is possible to simulate oil painting or water colors using a computer), most quality sandcarving is done using freehand line drawings, with the artist incorporating the limitations of the medium into the design, as it develops. 

Once the design is complete, a mask must be constructed to prevent the abrasive from carving the glass in areas to be left "clear".  Two choices here are to:

1.  Use a hand-cut or plotter cut mask.  Until the late Twentieth century, these were tediously cut from various "resist" materials, using a sharp knife.  The detail in the image was determined by just how fine a cut the artist (or more likely his underpaid assistant!) could cut the mask.  Prior to cutting the resist, the design is transferred to the "resist" or mask material.  Usually this is by either drawing directly on the resist or with carbon paper.  The mask is cut with a knife, stuck to the glass and then select pieces are removed sequentially from the areas to be blasted.   In the case of multi-stage carving, the mask is peeled in pieces as the carving proceeds.  For modern production work, a computer driven plotter/cutter automates the task, and greatly improves accuracy. 

2.   Use a photo resist.  This is a new process that uses a photographic technique to transfer the line art to an Ultra Violet light sensitive material.  This is done using an image of the line art, and Ultra Violet light to expose the water-soluble resist, causing the exposed areas to become insoluble.  The resist is then "developed" using a high pressure (usually 400 to 1000 psi) water spray, and attached to the glass.  At this point, the resist has a precise pattern of clear areas where the abrasive can attack the glass. 

Once the resist material is mounted on the glass, the glass can be abrasively carved in a blasting room or blasting booth ("glove box").  The blasting process can take from a few minutes for simple designs, to many hours for complex, multi-stage carved designs.  During the process, other techniques such as remasking and diamond burr engraving may be used to refine the image. 

The blasted image may be painted or gilded.  Many view this as "gilding the lily", since the as-blasted surfaces have a unique beauty without additional materials.

Finished glass work is often displayed using edge lighting, which accentuates the depth of the carving.

Other techniques

Laser Engravers

Laser engravers that can be used in place of the mechanical engravers do NOT work well on glass.  Some manufacturers have retracted their claims about this technique and it is rapidly falling out of favor.  The stresses introduced into the glass by intensely heating the glass in a small spot can cause problems weeks and months later.

Acid Etching

Acid etching using hydrofluoric acid to roughen the surface of the glass requires much less equipment than blasting.  It is simple, and can use the same masks and resists.  Used carefully and correctly, the materials can be used safely by adults. However the acid used is dangerous.  This is NOT an activity to share with your children.  The effects of the acid are not the burning associated with other strong acids, but it can travel through your skin painlessly and attack bone.  Rubber gloves and eye protection are a must.

Diamond Point Engraving

Engraving glass once meant scratching or stippling a pattern in the glass with a diamond.  Diamond point engraving of glass by hand is actually being revived as a decorating technique, but it is a very demanding art form.  What most refer to as engraving today is done by a computer-driven diamond burnishing machine.   This $2,000 to $25,000 machine looks like a cross between a plotter and a router.  A small rotating diamond bit  scratches a design on the surface of brass, plastic or glass.  A special jig holds wine glasses or bottles and allows engraving of curved surfaces.   These are used mainly for the trophies and awards industry.  

Wheel Cutting

Wheel cutting is the same technique used on your grandmother's cut glass or Waterford crystal.  Abrasive wheels, or diamond dust on copper wheels, are used to cut away the glass in the desired design.  Lead crystal, which is softer than most glass, is most often used.  The higher refractive index of the crystal also shows off the cutting better.

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