Notes on working with dichroic coated borosilicate

Milon Townsend

The following notes parallel the webinar presentation you have been able to enjoy. Some of the information will have been presented, but much of the following will be insights that I was unable to fit into our short 2 hour format. I am in the process of writing ‘Flameworking, Volume II’, which features an extended section on working with dichroic coated glass.

I use only CBS (Coatings by Sandberg) dichroic coated glass, proved to me many times over for its durability and consistency. Contact your favorite distributor and be sure to request CBS coated dichro. It is very resistant to burnout, and the color palette is quite wide and varied.

Boro plate glass is a relatively unknown element in our field, since getting is has been pretty costly, up until now. I felt strongly that it made no sense to clue you in a radical and exciting new way of making dichroic galaxy cane if you wouldn’t be able to get your hands on what you needed to do it with. I have arranged with ABR Imagery that they will carry boro plate glass in 6.5 mm and 9 mm thicknesses, at a very reasonable price. www.abrimagery.com

If you’re interested in the 2”and 3”thick chunks that I use for bases on some of my work, with dichro melted into the bottom for effect, please contact me. See the email address at the bottom of the next page.

The torches that I typically use – Mini Milon by Nortel and CC and CC+ bench burners by Carlisle are all or partly pre-mixed, giving them an aggressive flame and intense quick heat very suitable for working with boro. You will find that the triple mix and surface mix burners will tend to burn out the dichro even less than the torches that I use, and that you should have very good success.

Please take the time to cut yourself a bunch of little strips, something like ½”x 2”, and let yourself experiment freely. Don’t worry about burning it out – just work with it until you become comfortable with the material and the process. It is in fact necessary to heat the coated surface directly sometimes, so you need to feel OK with doing that, based on your own experiences.

You’ll also notice that different colors behave differently. Some colors will flake off more than others; some multiple coating colors tend to burn out a little more; narrowly patterned sheets tend to burn out along the edges of the patterning where the coating stops and starts again.

Pre-heating strips or pieces in your kiln (1050˚F - 1125˚F) will keep from wasting any due to cracking when you start using the piece. Putting the partically used piece into the same hot kiln will keep it from cracking when it cools down, and prevent waste there as well.

I find it generally useful to establish a heat base in the dichro prior to application or heating it on the coated side. You can either pre-heat it in your kiln, or attach it to a pontil and run the uncoated side up and down in the flame until the piece is pre-heated and maybe even a little soft. Heating it on the coated side at this point will create little or no burnout, as long as you don’t use an extremely hard, sharp oxidizing flame directed at one point on the dichro coated glass.

The coated side adheres a little less well than the uncoated side, since there is a thin layer of in between the two surfaces being joined.

When cutting dichro with a wheel type glass cutter, be sure to score it on the uncoated side. This will give you a better break. Do be careful, though, that you don’t slide the glass (coated side down) around on the cutting surface, since it is very likely that there are small glass shards on the surface that will scratch the coated side. Cutting borosilicate glass (whether the plate from which to make the sandwiches or the dichroic sheet itself) requires about 60 lb. pressure on the cutting wheel, as opposed to the 8 lb. pressure needed to cut other glass.

Please contact me at: [email protected], should you have any unresolved questions. I’m sharing the information about dichro as I’ve found it useful in my own work, and my desire is that you succeed in implementing these methods into your own artistic vocabulary.

For information on ordering stencils, or purchasing a system for making your own, contact: Rayzist Photomask, 955 Park Center Drive, Vista, CA

1-800-729-9478 www.Rayzist.com

DICHROIC GLASS

Dichroic Glass is an ultra-thin coating of metal and crystal, grown as a crystal structure on the surface of glass, using a highly technical vacuum vapor- deposition process. Originally produced for the Aerospace industry, science has joined with art and Dichroic Glass is now used by top glass artists in the industry. The main characteristic of Dichroic Glass is that it has a transmitted color and a completely different reflective color. Furthermore, these two colors visually change depending on your angle of view. Since there is virtually no absorption of light, the purity and intensity of color is unlike any other colored or on the market today.

THE DICHROIC GLASS COATING PROCESS

The two hour vacuum vapor-deposition process used to create Dichroic Glass, must take place in an airless environment, so large six foot diameter, stainless steel vacuum chambers are used (Each chamber is valued at over one Million Dollars). The chambers allow a controlled environment of pressure & temperature so that, when melting/vaporizing materials, the molecular vapor is the only material that is condensed onto the surface of the glass substrate. This process is much like the “fuming” process that a lampworker uses to fume or other onto an art piece, except the Dichroic Coatings are performed in a highly controlled airless environment and it takes a scientist and an engineer to maintain and manufacture this very technical product.

The detailed coating process entails complete precision. First, the glass must be cut into circles so that the full run of six sheets can individually rotate while the coating process takes place (The rotation of the glass allows a more consistent coating from one edge of the sheet to the other). Next, the circular sheets are rouged with cerium to remove debris from the glass surface. Then the sheets are cleaned once again with a solution of Isopropyl Alcohol and mild soap detergent to remove water spots and/or calcium buildup. Just before the technician loads the glass into the chamber, it is final cleaned with pure Isopropyl Alcohol and blown off with dry nitrogen to knock off any specs of dust and/or debris that might have settled onto the surface. This painstaking cleaning process is essential to the quality of the coating and allows the vapor to better adhere to the glass surface. The glass is now ready to be secured onto the spindles within the chamber.

Once the glass is loaded into the automated chamber and the large door is secured shut, six separate computer systems take control of the run. The mechanical pump starts evacuating the air within the chamber, the heaters start to heat the chamber to approximately 300 degrees Fahrenheit and the rotation motors kick in. Compressed air lines are used to open valves and move shutters within the pressurized chamber. Water cooling is continuously supplied to the crystal monitor (measures the material being deposited onto the glass), the electron beam gun crucibles where the material is held waiting to be evaporated, the walls of the chamber and the compressors that generate the cooling for the cryo pumps (The air freezes as it is removed from the chamber). During this “pump down sequence”, we perform a Plasma Discharge Glow Cycle that further cleans the glass and metal tooling inside of the chamber. The “Glow Cycle” is generated by using high voltage within the chamber to create an electrical field of ions around the glass substrate. Pure oxygen is bled into the chamber during the Glow cycle to remove any left over hydrocarbons on the surface of the glass by a process of oxidation. Also, the bleeding of gas into the chamber during the glow cycle has a secondary effect of “ Impinging cleaning”. The glow gas entering the chamber is coming from a higher pressure source and enters into the vacuum at high velocity, striking the surface of the glass causing particles on the surface to dislodge. By the time the glow process has ended, the mechanical pumps start to labor under the stress and pressure of the chamber as it drops well below atmospheric pressure. This is when the computers signal the cryo pumps to kick in. The cryo pumps have large surfaces at a very cold temperature (approx. 12 degrees Kelvin, which is –438 degrees Fahrenheit). When the molecules of air from the chamber enter into the cryo pumps, they freeze on the very cold surfaces and become captured. The airless environment created within the chamber puts over 128 tons of pressure on the chamber walls. For scientific buffs, the pressure needed for coating is less than 10 to the –3 Torr.

The conditions within the chamber are now viable to start coating. At the base of the chamber, the Electron Beam Gun begins to power up. The 10,000 volt E-Gun beam of electricity bombards the small crucible filled with Quartz Crystal and vaporizes it. Looking through a small porthole on the side of the chamber, the technician uses a joystick to move the Electron Beam in and around the pot of material so that the Quartz vaporizes smoothly and evenly. The light that the E-Gun produces is blinding so the technician looks through a special glass lens much like lenses used for arc welding. The heat produced from this reaction causes the vapor to rise upward and attach to the rotating glass above. The molecules of vapor condense on the surface of the glass, forming a micro-thin layer. Once the optimal thickness of this layer of Quartz is achieved, the system shuts the E-Gun down just long enough for the pot of material to automatically rotate around to expose a second small crucible filled with metal oxides. The E-Gun powers back up and the Oxides are now vaporized, float upward and attach to the glass surface above. This process is repeated up to 30 times to create the final Dichroic coating. The Dichroic Coating is a “sandwich” of many microscopic layers of Quartz and Metal Oxides that filter the visual spectrum of light in a specific, scientific manner. We select what color to produce by varying the thickness of the coatings. The thinnest standard coatings are the cooler colors and the thickest standard coatings are the warm colors. This light filter that we have created is known in the scientific world as a “ Interference Filter”, or what we call Dichroic Glass.

After the final layer is applied to the glass, the controller system signals the start of the Venting process. Air must be released back into the chamber to allow the technician to open the chamber door and switch out the glass for the next run. The air is bled slowly back into the chamber over a period of about 30 minutes so that the warm coated glass is not thermally shocked/broken. Once the atmospheric pressure in the chamber is equal to the normal pressure on the outside, the chamber door automatically opens and the glass is removed and shelved for later inspection.

The inspection process is lengthy and thorough. Each sheet is first visually inspected for cleaning issues such as inclusions, dust spots, watermarks, etc. Then the coating thickness is measured. Since the coating is only about 30 millions of an inch thick, it cannot be mechanically measured. It must be measured using a Spectra Photometer that shines a beam of light through the coated surface and produces a bell shaped curve on a computer screen that will depict what color spectrum of light is passing through the coating. What spectrum of light doesn’t pass through is reflected and this reveals the Dichroic effect of transmitted color versus reflected color. The computer generated curve is measured against a visual color spectrum graph and the Dichroic Color and vibrancy is confirmed. Then a small glass test piece from each run is kiln fired to a full fuse temperature to confirm color, color shift, texture, and durability. Random runs are tested even further. This further testing might include lampworking, glass blowing or aggressive kiln firing programs. After all this extensive inspecting and testing, the sheets of glass are finally worthy of the CBS sticker.

Similar Dichroic coatings are created for many other industries, such as fiber optics, anti-reflective lenses for binoculars & telescopes, laser technology, color filters in stage/concert lighting, camera filters, hot & cold mirrors, semiconductors, superconductors, data storage, night vision, display technology, etc. CBS produces specifically for the artglass industry and therefore we maximize purity and vibrancy of color. By dissecting the visual spectrum into a Dichroic Color for every 7% change in color spectrum, CBS has created a Standard Color range from Violet to Red. Other coating companys might produce coatings in the non visual range, like ultra violet and infared red applications but CBS sticks to the “visual spectrum”. By stacking/coating two colors together during the coating process, we can create Premium colors such as and Magenta as well. These coatings are twice as thick as our Standard coatings and allow us to produce more colors, much like mixing paints to produce a new color. Patterns are created by using metal to block the coating as it is being applied. Metal that is butted up against the glass substrate will create a sharp distinct line of coating versus no coating, but metal that is suspended away from the glass, will merely “shadow” the coating as it is applied. The shadowing makes the depositing vapor varied in thickness and thus, creates rainbows and color shifts on the surface.