Glue Chipping


Authors: Pat Mackle


Revised: August 03, 2005


Back in 1980, in my quest to learn glue chipping, I was fortunate to meet a woman whose husband owned an old glass sign company in L.A.. His grandfather was partner to a glass sign company in the 1880s in Chicago called Rawson and Evans.  Their glue chipped, beveled and gilded advertising signs are now highly prized and collected today.


She gave me a copy of a written note given to her son by her husband in his hospital bed in the 1960s detailing his procedure for glue chipping.  It mentions mixing the glue as we all know, but of significance was his insistence that the glue always be re-used and never thrown away, and that the glue becomes better and stronger with use. Small amounts of new glue were added only as needed. The used chips would be put in a metal pail and crushed with an old wooden bat. The glass falls out. Also, I noticed that these chips re-dissolve in water faster than fresh glue granules. 


The applied glue was then allowed to dry slowly until it turned hard and transparent. Then it would be gently heated to remove the final moisture from the glue causing the glue to crack and peel bringing the sand blasted glass surface off with it.  Their set up for drying was very simple. It consisted of a raised wooden slat table with up-right posts against which the glass panels were leaned allowing the chips to fall to the floor. Two old fashioned gas burners were placed on the floor at each end on a low flame and an old tarp with holes was placed over all the glass panels holding the heat yet allowing the final moisture to escape. Upon returning in the morning all the glass would be chipped, ready to be soaked and cleaned in preparation for decoration. This company was known for its fine chipping consistency and control.  Using this information as a guideline and after several weeks of underdrying, overheating, broken glass and much heartbreak, I achieved success in a damp one-car garage in the middle of one of California's wettest seasons with water running in under the garage door and an order due of 300 1/4" oval etched and glue chipped door lights. Can you say "Mission Impossible?"  The winning combination was a small metal Sears lawnmower shed, inside, a crude wooden table frame, and a small low powered portable electric bathroom heater with a small built in fan. I couldn't believe my eyes when I opened the door to find all the glue chips scattered on the floor and I had a good even chip, 40 panels at a time.


Some important things I have learned:


   - There are different grades of animal gelatin glue. Some will not chip well at all. 


   - Measure carefully, it is very important that the correct amount of dried glue per square foot be achieved, keep glass level.


   - The coarser the sand, the better the chip. Don't use finer than 100 grit.


   - Apply your glue as quickly and evenly as possible. This makes for a fine and even chip. It helps to warm the glass so that the glue will flow out evenly and not jell into different thicknesses, as thin areas will chip sooner and thick may never chip at all.


   - After applying the glue, allow to dry gently. Forcing the glue to dry will cause it to shrink and curl prematurely before it has securely made a strong bond to the glass surface causing unchipped areas. If you notice the beginning edges of the glue begin to pull away without glass coming with it you are drying it too fast! You are missing a most crucial stage! The animal glue is no more than a molecular sponge which adheres to the glass. As it dries the shinkage and bond become stronger than the glass which has been further weakened by tiny sand blast fractures.


   - The key to chipping is to apply the glue well, allow it to dry evenly and then place it in an environment that has less moisture than the surrounding environment. You needn't use sunlight or spend money on desiccants which are quite actually overwhelmed by high moisture and are actually designed to remove and maintain low amounts of humidity in packaging. You would do better to invest in a small electric dehumidifier sold by Grainger. At least with this you can see the moisture collected in the water collector.


Big production glue chip companies don't use expensive desiccants, but instead favor large commercial dehumidifiers. The goal is warm, dry large volume gentle air flow to achieve nice even repeatable chipping in a reasonable amount of time.





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