Glass marking dates back to the seventeenth century when English glassmakers would mark their works with a symbol. While trademark identification still makes up many glass marking applications, today, more and more manufacturers are marking their products with lot codes, part numbers and date codes.

Indenting/Molding
Etching
Printing
Contact Printing vs. Ink-Jet Printing

The advantages and disadvantages of marking technologies are determined by their effect on the material or substrate. Applying a mark requires changing the finish. This is done in one of three ways:

• Indenting/Molding or displacing the surface
• Removing or etching the surface
• Adding ink to the surface

Indenting/Molding
Due to the fragility of glass, indenting is not a marking method usually associated with this industry. It is however one of the most commonly used methods. In the case of molded products, most molds are indented or engraved with primary identification such as trademarks, part numbers and patent numbers. Inserts can be used for date codes or recycle information. In the case of Insulated Glass, spacers are often indented. Here the mark can be stamped into the aluminum as part of a cut off process or roll marked into the strips as they are extruded. Indented and molded marks are the most permanent of the methods of marking. This is because the marking can not be altered without destroying the product. Indenting can be as simple as the methods described above or more sophisticated using a computer- controlled carbide stylus to indent marks one dot at a time. This type of indenting process is often used for traceability marking because it easily applies variable information.

Etching
Etching is a process that involves removing a small portion of the substrates surface in a set pattern to make a permanent mark. Technologies used to accomplish etching include acid etching, Airgrit™ or stencil blasting, and laser. The use of acid is slow and difficult to control. It is very effective for decorating and marking large areas but not practical for coding and production marking. Airgrit is a process which uses a rubber mask or stencil, through which an aluminum oxide grit is blasted under high air pressure. Airgrit differs from sandblasting in that the grit is controlled and re-circulated back into a enclosed hopper. This process is widely used in Tempering Plants, Laminating Operations and at Window Manufacturers. Machines can be a simple bench top style or fitted into a cutting table before washing. Automated systems require that the glass stop and a good seal is made between the glass and mask to prevent a fuzzy mark and grit leakage. Used to put Trademark, specifications and monthly date codes in a small area, the process is low cost, fast and easy to operate. All etching processes leave a frosted permanent mark.

Airgrit® Dry Etching Systems
For permanent marking of lenses, glasses, windows, automotive glass, test tubes and other glass products, Airgrit system produce a frosted impression on the surface of flat or round parts by blowing a fine grit through a stencil-like rubber mask. Bench-top, under-the-line and portable models are available. Without employing acids, dry etching is a safe, economical method of marking.

Printing
When printing a mark, ink is being added to the substrate. Printing, with the application of ink, introduces new considerations such as color and adhesion. Color is used to emphasize or make a mark more visible to the end user. Conversely, some inks are made to appear invisible except when subjected to certain conditions such as UV light or moisture. Because a printed mark is being applied to the surface, adhesion is often an issue. When mark permanence is desired, it is important to determine what substances the end product will be exposed to such as solvents, cleaners and finishing operations. If it is meant to be temporary, considerations should be made to when and how the mark will be removed. Many of these characteristics are controlled by the selection of ink. Inks are usually designed in conjunction for specific application technology. There are several printing technologies from which to choose.

Automated Flat Glass Marking
Looking to replace silk screen printers, many glass manufacturers came to Matthews to design a more versatile system to reduce costs, while maintaining a high-quality mark. Many glass manufacturers now mark their product with their trademark, part number, size and type, and an interchangeable date and batch code using Print-A-Mark™ Offset Printers. The printer is motor driven and integrated directly into the production line. The system uses adhesive-back rubber dies that contain all the vital marking information that appears on the glass. Ceramic frit-type inks have been developed, not only to work in the offset printer, but also to fuse to the glass during tempering to make a permanent mark.

Some manufacturers have used Matthews Jet-A-Mark® Drop-on-Demand™ Ink-Jet printers to code information on tempered flat glass during the production process. This application uses a gentle touch printhead that does not distort the type resulting in clear, crisp codes.

Contact Coder Marks Tubes and Small Glass Products
A reciprocating printer, the Contact Coder can be used in-line for intermittent coding operations or as a stand-alone marking station. A special glass marking ink withstands high temperatures associated with tempering. The unit uses a gentle touch printhead that does not distort the type resulting in clear and crisp marks every time.

Small Character Ink-Jet Printing on Glass Bottles
Lot codes, date codes and expiration dates are found on many glass products, especially in the food & beverage industry. For today's fast-moving bottling lines, Continuous Ink-Jet Printers code products at speeds up to 1400 fpm.

Contact Printing vs. Ink-Jet Printing
The first distinction is whether the print will be contact or non-contact. Contact technologies include silk screen, offset, direct, pad transfer, and reciprocating. Non-contact printing technologies also known as ink jet include Continuous InkJet, High Resolution InkJet, and Drop on Demand. In all cases, ink jet characters are formed by generating a series of dots. One key advantage is the elimination of the need for printing dies, screens or cliches. There is also the advantage of being non-contact which allows the printing of uneven surfaces. As the characters are a dot matrix design created from a single head, printing requires the movement of the either the marking head or the substrate. Ink-jet is well suited for printing a one or two line of text on to a moving product. Ink jet technologies vary by print resolution, throw distance and line speed. Most ink-jet printing is black, but over recent years, there have been great strides in the development ink of colors and inks designed for specific applications.

Common reasons to choose a contact method over ink jet are print resolution, wider selection of inks and colors, and the ability to change colors in the same printer. Contact printing technologies are used for identification as well as decorating as they are both suited for multicolor printing. Offset, direct and reciprocating printing technologies are one color processes and commonly used for identification. The offset and direct printers are designed to mark in line on either the top or bottom of the product. These units are commonly used on continuous extrusion and web lines. For registration of individual sheets or parts, the printers can be power driven from an electric motor or installed within the production line. A clutch signaled by a photo eye or PLC releases the printer to make one mark. Offset and direct printers are commonly used on float lines. These printers will use a wide variety of inks including frit-type inks that will become permanent after tempering. Marking normally consists of several lines of text that include names, trademarks, sizes, specifications, and monthly date codes. Reciprocating coders were originally designed for package identification but are now being heavily used in industry for traceability and operational codes. They can mark either a moving or stationary mark with either single or multiple line text. They are especially well suited for color code changes as most use a cartridge type ink supply. Because of their size, simplicity, and low cost, they are easily integrated into most production facilities.