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Laser-Engraved Surfaces

by Dick Lehman

I can hardly remember a single occasion during the past 20 years of my pot-making that I haven't cringed and grimaced — as least inwardly — at the repeated requests from customers to "deface" my pots. What does Aunt Tillie's birthday, Fred and Jean's anniversary or, would you believe, "Best-of-Show" goat breed have to do with my artistic statement? Most of us who work with clay inevitably, incessantly receive these requests to personalize our ware for the perceived needs of our customers.

If you are quiet, and really concentrate while putting your ear to a ball of clay, you'll likely hear the corporate baleful moan echoing from the generations of potters who have tried, each in their own way, to answer these thorny requests with integrity and respect. Potters and clay artists have taken up residence at every conceivable point along the spectrum of responses. Some have said "yes," and embraced the opportunity as part of customer service, financial security and niche marketing. Others have taken these petitions on as a design-integrity challenge. Still others have hoped against hope that in servicing these kitsch-prone pleas, the integrity of well-made, handmade pots would overtake their customers with such power and vision that they would know better than to ever ask again.

Some have compromised their better judgment and complied almost against their will, perhaps to please Aunt Sally or Grandma Mabel. Some have turned customers away with a wince: "Sorry, I just don't do those kind of things." Others haven't been so kind.

Although I still cringe and grimace, my spot along the personalizing spectrum has largely been one of trying to respond positively to my customer, if I can. I maintain a sense of hopeful naivete, trusting that with a little gentle nudging, maybe next year my customer will conclude that Aunt Thelma will remember her own name and her own birthday without having it splashed across one more mug. I hope I might be convincing when I suggest to my customer that the gift may be as-well (or better) received if the important names, dates and particulars show up on the bottom of the pot (if at all), instead of emblazoned across the side in billboard fashion. And I hope that business folks will see it as a progressive suggestion when I remind them that their employees will remember where they work and are not in need of being reminded; that loyal customers may prefer a well-made pot over an alleged gift of thanks that has been turned into a self-serving advertisement.

Still, in the face of all my gentle nudging, some people need products that are personalized. They need them because, well, they just do! Businesses, schools, corporations, clubs and churches have need of products that advertise, recognize, promote, and symbolize. Nothing I say will ever change that, nor in reality, would I want to. For these important occasions and promotions, I do prefer that these folks choose handmade products rather than commercial slip-cast ware.

So it is that I am always on the lookout for better, classier, less obtrusive ways of including personalized information on products. I have tried many of the processes that many other potters have tried, including drawing, painting, silk screening (see the CM portfolio "Freedom to Experiment" by Les Lawrence, April 1993; and the CM article "Silk Screening Slips" by Marvin Bartel, March 1973); stamping greenware and filling with oxides (see "Stamping Made All the Differencne" by Jasper Bond in the May 1988 CM); stamping followed by glazing, which accentuates the calculated irregularities of the impression; and decals (see CM's two-part article "Making Ceramic Decals" by Jonathan Kaplan, April and May 1975). Recently I discovered another avenue that may be of use to others in the clay community: laser engraving high-fired pots.

While talking to a friend who regularly has a considerable amount of wood products laser engraved, I wondered aloud about the potential effects of a laser on a fired glaze. She offered to take several pots with her to the engraver. Of the two samples I sent, the results were quite different. The opaque white glaze was simply etched, and the engraved area barely visible. But the glossy green glaze had a distinct bronze color wherever the laser had engraved and re-melted the surface. Within a week I had tested all my glazes. I discovered that five of them responded with color change when the laser engraved the surface.

When I began investigating this process, I knew little about lasers. I know only a little more now. But here are a few things to describe the process in broad strokes. Laser engraving is accomplished by using a beam of ultraviolet light, concentrated to a point approximately 0.006 inches in diameter. Most of us have probably seen wood items with intricately engraved designs. Other common applications in industry and manufacturing include laser-engraved designs on glass, acrylic, leather, painted metal, and anodized aluminum.

The pulse and intensity of the ultraviolet beam can be controlled by a computer. Many systems use standard graphics software such as Corel-DRAW! or GeneriCADD to provide both control and flexibility in type styles and engraved images. Existing computer (digital) images can be incorporated into the engraving as well. Camera-ready art, hard-edged graphics, even photographs can also be scanned into the computer for engraving.

The laser beam moves in a raster and/or vector mode to produce the image, while the "workpiece" (pot) says stationary. The machine I utilize accommodates a maximum workpiece of 11 by 17 inches, with a maximum workpiece thickness of 7 inches. Because the laser must be focused in much the same way that one might focus a photographic enlarger, relatively flat products (tiles, plates or platters) present less challenge than cylindrical objects (mugs or pitchers). To accommodate the curve of a mug laid on its side, the effective engraving area is limited to approximately 1 x 1 inches before the laser is "out of focus" to the extent that it no longer affects the surface of the glaze. For cylindrical forms to be engraved across a broader area, the piece would need to be repeatedly rotated while maintaining some registration.

A very recent development in laser tool design is the production of a chuck-like device, which will center a symmetrical cylindrical object and turn the object while a stationary laser head pulses. This additional technology will allow, in theory, for cylindrical forms to have full 360-degree images printed. (I have not yet had access to this tool in my applications.)

But what actually happens to the surface of a glazed piece during laser engraving? And why do some glazes "work" while others do not?

A laser expert, a physicist and a chemist would each likely give us different answers to these questions — answers we eventually should explore. Unfortunately, I am none of the above. But let me tell you what I do know, and about some of the observations that I have made.

On high-fired (Cone 9-10) reduction glazes, the surface of the glaze is always etched by the laser. That is to say, some of the surface material has been removed by the laser. If you rub your fingers across the surface of the glaze, you can just barely feel the contours of what you are seeing.

If you watch the laser operate, you will see pulses of white light at the intersection of the laser beam and the glaze. I have been assuming, based on the color of the heat that is generated (white), that the surface of the glaze, in addition to being partially removed, is being re-melted in a strictly localized area. (More on melting and fusion later.)

Light-tone matt surfaces, and especially glazes with rutile as a major colorant (4%-8%) seem most "color responsive" to the engraving process. Gold glazes change to bronze, pinks to dark mauve, light blue changes to dark blue. Two of the recipes listed in my CM article "Stealing Ideas," June/July/August 1993, work well: Rhodes 32 with Rutile and 2-D Blue. One of the gloss glazes (Mark's Special Glaze) in the same article is most striking, changing color from a glossy "seafoam green" to a rich, deep matt bronze in the engraved areas.

I would pass along one word of caution regarding the use of a laser on glazes that have significant crazing (as fluid glossy glazes sometimes do). Be sure to do some post-engraving testing of the surface to see if the glaze retains its integrity. Since the laser disrupts the surface tension, and actually removes some glaze material, badly crazed glazes may chip away or fleck off at the edge of the engraved areas. (The post-engraving testing is, of course, recommended for all glazes, but especially for any with crazed surfaces.)

In my experience, white and very light-colored glazes with glossy, satin or matt surfaces are etched at the points of engraving, but there is no color change in the glaze. Likewise, iron-saturated glazes like traditional temmokus experience a textural change at the point of the etching, but no perceptible color change. Glazes whose colorants are predominantly cobalt or chrome act similarly, regardless of surface. (Obviously, the matt texture of the engraved area is a bit more noticeable in contrast to a glossy-surfaced glaze than when the glaze has a matt or satin surface.)

Assuming that the glaze re-melts during the heat response of the engraving process, I wondered if the laser would melt a raw glaze and fuse it to the pot. I tried a normal dipping application of a temmoku glaze on a bisqued pot. (I regulate the specific gravity of our glazes by always checking with a hydrometer.) As the laser engraved the raw-glazed surface, the affected glaze changed from the brick red to the expected shiny chocolate brown. A visual check with a high-power magnifier, prior to touching the surface, revealed that the glaze had indeed melted and was fused all along the route of the laser. Touching the fused area, however, brushed it right off the pot. Only the surface layer of the raw glaze had melted.

Our normal application process had created too thick a coating of glaze for the laser to melt completely, so there was no fusion to the bisqued clay. Increasing the laser pulse and intensity, then repeatedly addressing the same surface area did seem to increase the mass of melted glaze, but did not fuse it to the clay.

I suspect that with careful monitoring it would be possible to regulate a glazing process that would apply just the right thickness to the pot's surface so that the laser would both melt and fuse the glaze to the clay. My hunch, based on my limited experience to date, is that the amount of glaze needed would be very small, and that traditional dip glazing would not fulfill the uniformity-of-application requirements. (Variations in the porosity of the bisqueware would also have a major impact on any dipped glaze application.)

One can, however, dream further. If one solves the application problems and it becomes possible to fire and fuse a glaze onto a bisqued pot, one could theoretically make repeated applications of different color glazes (washing away the unfused raw glaze after each step). With some registration procedure, it would create a kind of color "fusion-printing" process using fired glazes in almost limitless detail.

I have also tried staining bisqued pots with a light iron oxide was prior to subjecting it to the laser. The minute amount of iron oxide on the bisqued surface is removed in the laser engraving process (along with a bit of the pot), leaving unstained areas on a stained "background." Firing these pieces produces a light image on a dark background. Here, the laser "cuts" through the printing medium and the printing medium is removed, providing yet one more way of using the process.

I can think of a number of other approaches to the "fusion-printing" style that might be pursued. One might brush liquid high-fired glazes or a liquid high-fire stain over a previously-glazed and high-fired pot to see if one could more easily monitor the thickness of application on a nonabsorbent surface. The raw stain/glaze could then be engraved/fused, and the unaffected areas washed away.

One might also try applying liquid low-fire glazes or lusters over previouly-glazed, high-fired pots. The relatively high predictability of color with low-fired glazes (and potentially lower fusion temperatures) might make this just the right medium for laser etching, if the application and fusion problems can be solved. I think it is worth a try.

I have almost as many questions as I have experience-based answers regarding this process. The possibilities are quite expansive. I trust that you will humor my forwarding some of these ideas prior to thorough testing. While I have interest in all these possibilities, if one waited to share this information until all potentialities are explored, many others who may be interested in the process would miss the opportunity to join in the exploration and share in the discoveries.

It is equally obvious that I have explored only the more commercial applications of the parts of the process that I do understand. Of course, one need not avoid using laser engraving simply because it has commercial applications. Potters have always co-opted all sorts of commercial applications for artistic ends. Witness the innovative use of decals, silk screening, monoprinting and stamping. This laser information may be just one more instrument you store in your toolbox of resources.

This article is reprinted with expressed permission from the January 1995 issue of Ceramics Monthly Magazine, PO Box 6102, Westerville OH 43086-6102, USA; www.ceramicsmonthly.org

© Dick Lehman, 1995. All rights reserved.