How To Repair Colored Glass

	Stained drinking glass window of an angel by Louis Comfort Tiffany (above); and a item of the multi-layered construction which is typical of this blazon of work (below)
	A badly damaged lamb before (above) and after epoxy edge-gluing (below)

When involved in the restoration of south tained glass windows, it is of the utmost importance to retain as much of the original material as possible. Modern adhesives brand this task easier.

Stained glass windows expand and contract with variations in temperature. Equally they age the lead matrix deteriorates and the window begins to deflect (buckle), and the glass often cracks due to the stress and pressure level imposed by this bike.

Before new and avant-garde techniques were introduced to our arts and crafts, pocket-size pieces of lead were inserted in cracked pieces of drinking glass constitute during restoration. This is (still today in some cases) good practice, as the responsible craftsman retains the original glass, rather than replacing it with 'a good match'. The downside of this 'pb repair' is that it tin, and nearly likely does, interrupt the original design intent with the extraneous lead lines used to repair the cracked glass. Likewise, to make room for the lead between the two broken pieces, 1 of the two pieces may have to be slightly trimmed.

Although, over the years, the basic restoration techniques have non inverse much, they accept certainly evolved, allowing the careful and responsible craftsman to use these procedures for the benefit of the stained glass window existence restored. New materials, techniques and procedures have been introduced to our craft, specially over the by few decades, which have certainly fabricated a difference to the aesthetic result. These include: epoxy edge-gluing; silicone edge-gluing and copper-foil repair.

It'south important to know that these techniques differ from each other in reversibility, strength, and visual issue, and to make up one's mind the appropriate repair method to exist used on a case-by-instance basis.

EPOXY Border-GLUING

Edge-gluing broken pieces of glass with an epoxy produces a nearly invisible line. This aspect is specially valuable where focal points of a window such as a face have been damaged. Furthermore, epoxy resins can exist tinted with fine pigments to match the glass, reducing the low-cal manual and refraction. Epoxy can as well be used for infusing microscopic cracks.

This technique produces a very strong repair, but will most likely deteriorate in sunlight therefore requiring a secondary glazing to protect information technology from UV degradation. Epoxy is the to the lowest degree reversible of the three techniques and the about time consuming.

The type of epoxy resin used is not to be confused with epoxies establish on the shelves of local hardware stores. It is specifically made for glass conservation. Serpentino Stained and Leaded Glass studio has been using Hxtal NYL-1 epoxy, which is an ultra pure resin that seems to remain clear and transparent over fourth dimension and with exposure to direct light. Hxtal is supplied in ii liquid parts (A and B), both of low viscosity. It is to be weighed accurately, (ane part, by weight, of part B plus three parts, by weight, of part A). After the 2 parts have been weighed into a mixing jar, they must be mixed thoroughly. This role requires a lot of patience and must not exist rushed. As the Hxtal is mixed, numerous tiny air bubbles volition be seen to rise and pop. This is normal and to be expected, only be mindful that the bubbles will never totally disappear. The all-time way to eliminate the bubbles is with the use of a small vacuum chamber to suck the air out of the glue. This is called 'de-gassing' the gum. Small vacuum chambers are non very expensive and are quite useful.

Freshly mixed Hxtal has a very low viscosity. If it seems too thin, allow it stand (covered), and over a period of several hours information technology volition thicken. Thin Hxtal, however, volition penetrate cracks making them nigh disappear. The best results are obtained when the glass is warmed to most 49°C/120°F (a pilus dryer or some other heat source tin exist used, taking care that the drinking glass being repaired is not heated besides much or likewise quickly). Since edge-gluing of cracked drinking glass is performed over a lite tabular array, I turn on the light tabular array several hours before repairing the cracks. This will evenly warm the glass surface of the light tabular array, aiding the penetration of the epoxy into the cracked glass, as the heat from the low-cal table draws the epoxy into the cracks.

Hxtal sets slowly at about 24°C/75°F. It requires nigh one week to reach its final bond strength. Still, ordinarily information technology sets afterward 24 hours, plenty to hold the two parts together as long equally no stress is applied to the repaired glass. Any excess epoxy should be removed with a sharp razor blade. The use of solvents is not recommended as they may seep through the epoxy and could accept a long-term event on the repaired piece.

SILICONE EDGE-GLUING

Silicone has very different backdrop from epoxy and provides a useful alternative for edge-gluing. This repair technique has the lowest strength of the three methods and should be used when a flexible articulation is desirable. For example, in situations where the window will be nether continuous stress or in the case of plated, multi-layered windows such equally ones designed and fabricated past the American renowned artists John La Farge and Louis Comfort Tiffany. Every bit all components of a edifice aggrandize and contract, so practise stained glass windows. In the case of plated, multi-layer windows, as drinking glass is stacked on acme of each other, during the expansion/contraction wheel it is best to have a repaired crack that flexes with the expansion phase, so that it can return to its original position unaltered post-obit the wrinkle phase of the cycle.

	Copper foiling, before (in a higher place) and after repair (below)
	Copper foil beingness applied

One of the benefits of using silicone to repair cracked glass is that information technology is hands reversible. A sharp razor blade and some acetone will easily remove the silicone from the edges of the glass. An important gene to be understood is that silicone repair (edge-gluing), is not the same every bit smearing silicone over the surface of the drinking glass, thus roofing the crack. Silicone is almost equally articulate as epoxy, but information technology refracts low-cal differently, making it detectable at times. The same coloured pigments used with epoxy, tin can be used with the silicone method reducing the light transmission and refraction.

I particularly like to utilize silicone for glass repair when working on opalescent drinking glass windows. A diverseness of small batches mixed with dyes of different colours can be easily mixed and manipulated to match the depth and hue of the opalescent glass and its marble-like striations and advent for which it is so well known. Unlike Hxtal epoxy, UV light does not affect silicone; therefore, a secondary glazing to the exterior is non necessary. For the concluding 12 years, I have been using, with excellent results, articulate silicone RTV 732 by Dow Corning. They supply it in small 2oz tubes, which makes it easy to work with, with little or no waste.

COPPER FOILING

The technique with the longest history is copper foiling, and this is by and large the best option when a slice of glass has only 1 or ii cracks. Copper foil is a thin adhesive tape which is practical forth each side of the croaky piece, trimmed to a minimal width on the surface of the drinking glass, and soldered. The Tiffany Studios introduced copper foil to stained glass craft where it was used for the manufacturing of their lamps as well every bit in their stained/ opalescent glass windows, particularly in and around organic, nature scenes. The craftsmen of the Tiffany Studios mastered the use of copper foil, producing extremely thin lines within their lamps and windows. Every bit restorers, we adopted their technique and material inside the restoration field. Copper foil produces a potent repair, is totally reversible and has a negligible artful bear on. The concluding repaired crack should take a sparse line no more than 1mm in width.

All three methods are recommended for the repair of cracked glass during restoration. It is the craftsman's responsibleness to examine the unabridged project and the relevant bug at hand before deciding which method to use on each piece. The most important gene is that each method is reversible. As a craftsman, I look forward to the futurity and for new techniques and materials to evolve in this 'old craft' of ours. As long as we continue an open mind, and are willing to acquire, nosotros will be able to restore and preserve our beautiful stained glass windows and their history for generations to come up.

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Source: https://www.buildingconservation.com/articles/stainglass/stainglass.htm

Posted by: malchowount1970.blogspot.com

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