Glass Surface Preparation
As with the traditional animal hide glue chipping process, the glass to be chipped must be roughened by sandblasting. The glass should be cleaned after sandblasting to remove residual sand and possible contaminates. The glass should be dry. The final chip design can be influenced by the surface preparation: a deep or very rough treatment usually results in a large area being chipped. A very light surface treatment usually results in a very small amount of glass being chipped off with large areas not being chipped.
Though a degree more difficult, it is possible to chip glass that has been acid etched. As with the sandblasted glass, the glass surface should be clean and dry prior to applying the polymer.
Glass chipped by the Chip-In-Place process can be tempered. The ability to temper chipped-in-place glass invites a variety of new architectural applications (shower doors, room dividers, windows and sliding glass doors).
Surface Masking For Containment
Chip-In-Place polymer can be used to chip entire sheets, specific areas, or highly resolved images. To chip entire sheets, the polymer can be applied manually (pour and allow the adhesive to spread), or applied using a coating machine.
During the Chip-In-Place process, most of the polymer will chip off the glass surface by itself. Occasionally, polymer at the very edge will not chip off. To facilitate easier clean-up after chipping, it is recommended that the surface perimeter of the glass sheet be masked (approx. 1/8th of an inch) with tape prior to dispensing. If the edge is masked, the polymer that doesn’t chip will be removed when the mask is peeled off. If the edges aren’t masked, the polymer remaining after the chipping process has concluded can be removed by scraping with a razor blade.
To chip specific areas or images in the field of each sheet, some form of masking and/or stenciling is required. Masking tape can be a very simple solution. After applying tape to the entire piece, a pattern can be drawn on the tape. Using a razor knife the pattern can be scored, allowing the tape to be peeled away from the area to be chipped.
The Chip-In-Place polymer is poured on or mechanically applied directly to the glass surface, and allowed to slightly overlap the edge of the tape. This ensures good edge definition.
As an alternative to masking with tape, the gel viscosity of the polymer may be used to outline a pattern, and create a dam that the standard viscosity polymer cannot flow beyond. As the gel viscosity polymer doesn’t flow, it is possible to apply the polymer to vertical and curved surfaces. This allows vases, bowls, pitchers and other 3 dimensional objects to be chipped-in-place.
Masks used during the sandblasting process may also be suitable for use as a Chip-In-Place polymer mask. It is recommended that a test be run to ensure that the sandblasting mask is compatible with the polymer.
Dealing With Process Variables
Chip-In-Place polymers are supplied ready to use; no cooking or mixing is required. Simply apply the polymer to desired chip area by whatever means is most convenient.
When a desired pattern is obtained, process consistency can be facilitated through the physical measurement of the applied polymer. Both the thickness of the polymer coating on the glass surface and the size of the contiguous area being chipped have a great effect on the final chip pattern. Consequently, both must be taken into consideration to determine the amount of polymer to dispense onto the glass surface each time. Two reliable measurement methods are: (1) calculating and maintaining polymer weight per in2, and (2) measuring actual wet coating thickness.
If the polymer weight method is utilized, it is important to consider the size of the surface area being chipped. The smaller the area being chipped, the less significant weight measurement becomes. Typically, more polymer weight (thickness) is needed for chipping smaller areas, almost to the point where too much is not enough. As the size of the area grows, polymer weight becomes very important to maintain. As total mass of applied polymer increases, the actual coating weight per in2 may need to be decreased to maintain a desired pattern.
A third variable affects chip pattern, and that is the thickness of the glass. Measurement values calculated from one specific glass thickness may not produce the same results on glass of a different thickness. Therefore new values must be established after the desired pattern is secured using a new glass thickness. After gaining some experience with the Chip-In-Place process, one can develop a feel for adjusting weight/thickness to compensate for changes in variables.
One important point to note involves the handling of the glass after UV curing and chip-in-place. Due to the significant heat generated during the UV curing cycle, and the stress built up in the polymer as it cools, large glass sheets and/or thin glass must be handles with extreme care to avoid breakage.