Cold Work – The Other Side of Hot Work

When you have guests everyone notices how pretty the table looks once its been set.  Rarely do we want to see how the table looks once all the plates and serving dishes are put away in the kitchen as piles of plates and bowls and cups and platters add up.  Everyone wants to enjoy the evening, but who wants to have to do the dishes?
In everything we do there is the less interesting yet necessary things that go into making the day, the experience, the object or artwork or craft object. In glass, most often you will see artisans simply blowing. its exciting, sexy.  So why NOT show this side of the industry to would-be customers?  You wind up seeing JUST the blowing end of things.  We all use the exciting ends of things to sell people on it. Its pretty rare to see the finishing end of glass work simply because its not the hot part, the fiery end of things.  Some assume it mustn’t be interesting to people because its not very interesting to THEM.
To do the work I need to do, I have to do finishing work, something we collectively call “cold work” which is when glass that has been blown has bottoms ground flat and brought to a fine degree of finish or polish.  This is slow, wet work with grinding or abrasive tools that  are lubricated  by a steady flow of water to slowly wear away layers of glass for the finishing work to be complete.  In principle it is the same as sanding or finishing a piece of wooden furniture or finishing an automotive panel.  You go from coarse to fine grit.  But that is where the similarities end.
What I am going to show you is a insiders look into the process of glass finishing.  It isn’t meant to be an exhaustive review of all the processes or tools possible in the process because there are many.  For our quick jaunt I am going to keep things limited to a horizontal flat mill that I use for grinding smaller things.  Cold work doesn’t get much press simply because its not as exciting or maybe as sexy as hot work.  It is, however, an essentially portion of the larger whole.
Cold work, as it is called, is the abrading of the glass surface in order to grind away sharp edges created from cracking off glass either from the blow pipe or from the punty ( a solid metal rod used to hold a blown piece of glass after it has been broken off the blowpipe in order to finish it). Cold work can be very direct in its method; grind away any sharp parts of glass so the glass is smooth and finished looking.  However, cold work can also be used to be an end in an of itself for creative expression.  Glass can be faceted or engraved as in the case of copper wheel engraving which produces colorful prismatic effects with clear glass and the presence of light. This is a tedious and time consuming process but it can also bring a glass object to a level of fire and sparkle that a smooth uncut surface does not have.  Facets might be cut or abraded into the surface of glass.  Imagery might also be ground into the glass, perhaps in reverse.  In some cases, cold work might be used to rind through color layers in the glass to reveal certain colors in the same way that South American Mola’s are made by laying down many colors of textile thread only to go back through and remove  layers of certain colors  to reveal the layers beneath them. Using this technique, one could blow a multicolored ball of glass with many colored layers, and upon cooling, take the ball and cut it apart and sandblast the colored layers away to create the appearance of, say, an animal or bird.  This technique is called Graal (pronounced “grawl”) and is effectively a way to create shards of glass which are then picked back up onto a hot gather of glass and reincorporated into a new piece where the shards are now hidden beneath a layer of clear crystal for all to see and wonder just how the designs got inside the glass.  So while cold work is itself very practical, it has an expressive side as well.  Having been an artisan who used cold work to create the only curved lenses that I know of in my paperweights and sculptures, I can attest to grinding being an expressive medium, albeit a time consuming and wet one.
grinding check sized
Grinding is done most often on a horizontal flat mill.  This mill could be an iron disc with loose grit dripping across its surface to create the abrasion, or more recently we also have diamond embedded grinding discs that keep the grit in one place and can be used over and over for many years before they wear out.  Grinding can be done with small handheld devices like angle grinders with diamond blades or discs with a water feed attachment as well as devices that look very much like bench grinders and also belt sanders.  The grit on these devices goes from coarse to extremely fine as the piece is worked at each grit until it achieves a fine level of finish. If you look at the grinder I am using in the photo above, you can see a flat disc that is turning with a hose that is feeding water to the center of the disc to help lubricate it. The grinder is basically a plastic housing that catches most of the water spray (but not all) with a powerful motor that turns the spindle that in turn spins the diamond discs which are all attached by way of a powerful magnet holding the abrasive disc in place.
This grinder spins at about 1400 r.p.m.’s and the diamond grit I use varies from a very coarse 45 mesh grit to an extremely fine prepolish disc that is in the area of 1200 mesh.  Final polish is accomplished with a felt pad that has a polishing compound embedded in it.  All of this is accomplished wet and makes observing the progress of the grind and finish a little tricky. But before I get ahead of myself, let me show you the grinding discs….
grinding discs cart viewWhat you see in the photo with all the discs arranged in a series of slots is a caddy I built years ago to keep my grinding discs for finishing glass organized..  I set it up near my grinder for ease of access to all of the different grits I might need during the course of a grinding session.
grinding discs closeupThis is a closeup view of the grinding discs.  You can see that some of the discs have a dot pattern across their surface.  These are clusters of diamonds that have been sintered into a nickle mini-disc that is then attached to a plastic substrate.  This plastic is then attached to a metal disc and the metal disc is then held to the spindle or wheel head of the grinder.
The dark brown discs are prepolish discs, the step necessary before final polish is done.  The rust colored disc is the final polish disc.
For the purposes of this post I ground some pieces without the usual protective equipment.  Normally I will use eye, ear and face protection when grinding.  The grinder creates a lot of noise for example, and sometimes glass can chip off from the work so safety glasses are useful at certain stages of the process.  As you might be able to guess, just holding on to the glass as the water used to lubricate the diamond and the glass is filled with small glass particles, it gets harder to keep a firm grasp on the glass.

grinding closeup sized

the bottom of a vase is examined for scratches as it is being ground

During the course of the grinding and finishing of a piece of glass, the object being finished will be taken through a series of different grit sizes in order to progressively create a finer and finer ground surface until the surface is so finely ground that upon being turned on a polish wheel, the glass is brought to a high level of polish.
cup grinding sizedThe tumbler that is being ground in the pictures that follow shows how the bottoms of pieces have to be examined to make sure that all scratches from the previous grit are worn away before moving to the next grit size.  If this is not done properly, the scratches from coarser grits can remain in the piece and wind up becoming polished scratches which appear as polished shiny grooves on the surface of the glass being worked. The purpose of fine glass finishing is to render the glass as looking like the rest of the glass around it so that one never knew that the facet or surface had ever been in such a coarse or rough state. When done properly, people do not notice the ground or finished surface except that it is part of a consistent whole.
cup check sizedIn some cases, surfaces are not brought to a high level of polish.  In my case, there are several very specific reasons for not bringing a surface to full polish.  I might want the bottom of a piece to be opaque to the rest of the world. I might want light to enter, but I might not want people to be able to view through the glass completely as is the case with highly polished glass.  In some cases I create diffusion filters in my paperweights so that when light is shot up from underneath them from light boxes, the light is softened and scattered,cup check 2sized creating a pleasing and soft diffuse light.  On some light boxes I note that the makers have done the same thing by providing covers for the lights that have sandblasted discs which are called diffusion filters. This achieves the same result and is sometimes necessary or wanted.  In some cases I may be making a piece where I have very specific color effects playing on the surface of a vase and I may not want the bottom of the piece to be ground so that other colors can be seen through the bottom of the piece so I might leave the bottom ground but only to a 600 grit, for example, which is a soft enough surface that it does not mar fine furniture.  IN another case I might have a tumbler or other object that I know will get a level of high use and instead of bringing the bottoms to a level of high polish, I might keep it matte in order to help hide any scratches or wear that might build up across the surface over time. I have observed that the scratched on a polished surface always look ten times worse than the same scratch on a matte or not fully polished surface.  The final reason for not bringing a piece to full polish is simple economics. If I am making an inexpensive item and want to keep the costs associated with those pieces down, I might, if the situation warranted it, choose not to bring some part of a ground surface to full polish.
When grinding I keep a circulating loop of water going in my grinder.  This recycles the water I use and has resulted in the savings of thousands of gallons of water over a ten year period. I do a LOT of cold work in my solid pieces and I was finding that I was going through twenty gallons of water every hour when I was doing my grinding.  By placing a small pump in the bucket I was able to reuse the water many times and I also was able to  capture the fine glass particles so they settled into the bottom of the bucket.  These fine particles actually get saved, dried, and then are put back into the furnace in order to re-vitrify them into solid glass again prior to land-filling them. What is important about the process that I employ is that when glass is ground as finely as I do in my finishing process, the chemistry of the glass becomes much more porous to the environment.  Doing this is my way of keeping the impact of what I do to a minimum for the environment and does keep leaching of heavy metals down to zero this way.
process pieces sized
The result of all of this is a double-win; I keep heavy metals out of the environment and I am able to save significantly on my water usage when grinding.  Doing this does mean that my grinding is more of a dusty affair for the simple fact that there is more glass particulate in the water since its being recirculated.  It does make the water feel more slippery or even soapy feeling, but it also means that I am keeping the glass out of the septic system.
When done with an eye towards detail, cold work can be used to enhance glass work.  It can be used to cut bevels into glass, it can be used to create interesting lines and other surface effects.  IN its least noticeable form, it is used to give the work a look of finish and to keep a rough area on glass from being noticed by completely removing it and returning the glass to a polished, sparkling pristine state.
Cold work isn’t the most glamorous part of glass making.  Its the part of the work that most people aren’t even supposed to notice.   In the same way that you would not consider having your guests stay and help clean the dishes after having had a fine meal at your home, so too you would not consider leaving a sharp hard surface for your customers to see without first grinding it away or giving it a look of finish.