Water Size Recipe for Glass Gilding

In glass gilding, a water size is the glue that adheres gold leaf to the glass. Made of water-clear gelatin and distilled water, it is essential for creating a brilliant gold mirror finish.  Of course, you can also apply gold to glass with oil size, if you want areas of a design to have a matte finish. Many gilders will use both water size and oil size to create a two-toned gilded letter or ornament (see the photo below).


The recipes for cooking water size are basically the same, with a few minor variations. As with any recipe, your key to success is to control the process. That way you can control the outcome. While there is nothing wrong with creativity, you often run into problems when you improvise.  Just follow the step-by-step directions below and get cooking.

  • Gelatin size is sold both in sheets, which are divided into diamond shaped pieces, and in capsules.  Soak two diamonds in a half pint of distilled water or four to five diamonds for every pint of water for 20 to 30 minutes. Only use distilled water to prevent any contamination that could cloud the gold.   (You can order sheets of gilder’s gelatin size atwww.letterheadsignsupply.com.)

If you are using gelatin capsules, you can substitute one 00 capsule for every two diamonds that you would use. During this time the gelatin will begin to soften.

Note: Mix the gelatin and the water exactly according to the instructions. More is not always better when mixing up a batch of water size. In most cases you should resist the temptation to add extra gelatin capsules to your mixture. Sure, strong mixtures create a strong bond to the glass.  Sometimes if it is too strong, it can make cleaning off unwanted gold from the glass very difficult.  Too strong of a mixture can also become hazy over time, lessening the brilliance of the mirror finish.  Too weak of a mixture of size, though, is worse than too much. A weak mixture can result in the gold leaf chipping and peeling.

  • Heat the water on low heat until it is steaming hot. As you gradually heat the water, occasionally stir the mixture using a clean spoon.
  •  Heating the water dissolves the water-clear gelatin. Once the water is steaming, continue to heat the mixture for one to two minutes, continually stirring until the gelatin has dissolved completely.

Note: Do not allow the water to boil. High heat will cause the gelatin to harden, ruining the size.

  • After heating, let the mixture cool. To ensure that the gelatin has dissolved and no globs are in the mixture, strain the size through a fine sieve.
  • For every half pint of water, add a drop of Ivory or Joy dishwashing liquid to the mixture. The dishwashing liquid will break the surface tension of the glass so the size will wet out the surface properly.

In the old days, gilders would heat the mixture on the job site using cans of sterno.  To avoid any potential fire hazard, you are better off making the size at home or in the shop and transporting it to the job site in a clean glass jar.

Water size does not keep well. Only make enough gelatin size for that day’s work. Do not store the size that you have mixed for that work day for the next day.   By that time, the size may have become cloudy.

While you can use water size in a cooled state, some gilders will warm it up on the job site, warmer it is, the faster it dries. On the job site, some gilders will warm the size with an electric heater. The warmer the size is the faster it will dry.  To accelerate drying, you can also warm the area that you have gilded with a hair dryer.

As seen on hingstssignpost.blogspot.com