Sunday, September 4, 2016

Seeking the Meniscus...Measurements Used in Gilding.

Often students will ask during the Traditional Water Gilding class whether the measurement of materials should be by weight or volume when preparing rabbit skin glue size, gesso, and clay bole. I usually preface my answer by first pointing out that I prefer the metric form of measuring as I find it more exacting. 

When I switched many years ago from the US table of measurements to metric I performed a simple test: I measured by eye what appeared to be an ounce by volume of dry rabbit skin glue and then weighed it on a metric balance scale for comparison. Each time I performed the test the metric equivalent  was different. That was convincing enough for me to make the switch to metric; I needed to match samples of gilded picture frame finishes as closely as possible and since there are so many things that can go wrong in gilding it's best to control what can be controlled and that would include the measurement and freshness of materials. 

The question of whether to measure by volume or weight is a little more complicated. The equivalency of measuring materials by either of these two methods depends upon the material. Water may be measured either by weight or volume (1 ML of water = 1 gram). So which is better, to measure water by volume in a Graduate or weigh it on a metric scale? To answer this let me illustrate that in the past when I chose to weigh dry materials such as rabbit skin glue and whiting on a metric scale I measured water by volume in a Graduate, keeping the beaker as steady and even as possible for accuracy. However, I inadvertently discovered one day that a specific amount of water that I measured by sight of volume did not equal the same when weighed on the metric scale.

The reason for the discrepancy is due to what is called the meniscus which is the curve in the upper surface of the water in the Graduate. A meniscus may be either convex or concave depending upon the liquid and the surface material of the object containing the water. Water and the use of a glass beaker or plastic Graduate will produce a concave meniscus as shown in this photo of colored water in a burette, the proper reading being 20 ML:

What this means in practice for gilders is that the proper measurement of water requires viewing the surface of the water through the measuring container straight on so that the meniscus can be seen; it is the bottom of this curve that determines the proper measurement. As an example, if you are seeking to measure 50 ML of water make sure that the bottom of the curve is at the 50 ML mark.

To discover how much difference there might be by virtually 'eyeballing' a certain amount of water in a Graduate I tested measuring by volume 50 ML of water without specifically looking for the meniscus but still seeking a measurement that seemed fairly accurate. I then weighed this amount of water on a metric scale with a result of 41grams! When making small batches of rabbit skin glue size or bole mixtures this nearly 20% variance could prove quite drastic, partially because we run the risk of using a glue size that is stronger than we think.

What we can learn from this is that we need to seek the meniscus of water if choosing to measure by volume. Considering the chance for error, however, it is simpler and safer to weigh the water on a reliable metric scale.

Friday, July 22, 2016

Choosing Oil Size or Acrylic Emulsion?

Q. What would be the reason to choose either oil size or acrylic emulsion when using a method of gilding other than traditional water gilding?

A. Oil size and acrylic emulsion, sold under such names as Water Based Gilding Size, Aquasize, or Wunda Size, are a form of mordant gilding. Mordant gilding employs the use of an adhesive to adhere gold, silver, or imitation leafs to a prepared surface. Other mordants include gum tragacanth, gum ammoniac, gum arabic, garlic, and glair (beaten egg white).  

The use of oil size, a form of mordant gilding, is commonly referred to simply as oil gilding. It's a specially formulated varnish which produces a satin to semi-gloss tone in the leaf. It does not produce the high luster of traditional water gilding but it has an attractive appearance of its own. It offers a durable finish and is used for both interior and exterior gilding projects.  

Oil size is self-leveling whereby the oil tends to smooth out after it's brushed on thinly. It cleans up with mineral spirits and so is somewhat messy to work with so be prepared to use rubber gloves, spirits, and perhaps some acetone in the cleaning of your brushes.

Oil size comes in different drying times ranging from 3 hour to 24 hour. In practice however, once a can has been opened the drying time becomes shorter and shorter. It's best to open the can, stir the size to bring the driers to the surface, and pour some into another container for use on your project. This way you can close the can of oil size and preserve its life.

The water-based sizes are much cleaner to work with as they only need soap and water for cleanup; just make sure you clean your brush once you're done as the size will harden and will require acetone to remove the dried adhesive. One of the benefits of the acrylic emulsions is that once it's applied to a surface it will come to the proper tack in about 15 minutes and remain properly open to gild for about 36 hours. The drawback is that it never seems to quite dry. A clear coat after 24 hours can help protect the gilding from this effect.

Acrylic emulsions have a brighter appearance than oil size but do not have the brilliancy that you can only get from traditional water gilding nor does it share its almost magical tone and glow. As for which size to use, oil or water based, it's important to know that most any high quality project which is not water gilded uses an oil size. That said, acrylic emulsions can provide a gilding option that is both quick and much easier for the beginner.

Saturday, July 16, 2016

About Traditional Gesso: Part Two

Smoothing away pinholes in gesso

In our last installment of the water gilding process we discussed an overview of preparing gesso, its function in sealing the grain of wood and allowing the gold leaf to be burnished. It is also of great importance to understand the relationship between the strength of the binder (usually RSG - rabbit skin glue) and its relationship to the filler (whiting - calcium carbonate). If the glue strength goes much beyond the 10% solution, the possibility of crack mechanisms in the gesso increases; likewise, if the glue strength is too weak, gesso delamination from the wood surface could occur.

Once the proper gesso mixture has been prepared and at least 5-7 coats have been applied, the gesso is allowed to sit overnight to thoroughly dry. It is then ready for surface treatment to provide a smooth surface.

There are different ways to smooth gesso, the most common method today being sanding. I like using 3M Tri-M-Ite sandpaper as it holds up well and cuts through the gesso efficiently. Primarily, I use either 220 or 280 grit, depending on the surface and how aggressive the paper needs to be. As a rule of thumb I recommend using as fine a grit as possible while still being able to effectively smooth the surface. If the finer 280 grit works well there is no need to use the heavier coarse 220 grit which will leave heavier sand marks which will later need to be removed. If starting with the heavier 220 grit, follow-up with a light sanding of the 280 grit and a light, final dry polish with either 600 or 1,000 grit wet or dry paper.
There are other techniques that may be used to smooth gesso. Cennino Cennini discusses in his 15th century treatise Il Libro dell'Arte (The Craftsman's Handbook) the use of 'little hooks' and a spatula to scrape gesso smooth as well as the use of water polishing with a damp rag. The use of a method called re-cutting, prevalent during 17th century France and Italy, is still used today.

Other treatments to gesso for aesthetic affect include incising and punchwork which create texture and often elaborate surface decoration as a compliment to the gilded surface.

Wednesday, July 13, 2016

About Traditional Gesso: Part One

Traditional Gesso is the combination of a protein binder (RSG), distilled water, and Calcium Carbonate - also known as whiting, or chalk - as a bulking agent. It is not to be confused with the oil-based or acrylic material sold today for use on canvases in preparation of painting.

Preparing a chair for gilding with gesso
The traditional gesso recipe used in water gilding performs two functions: filling the grain of the wood and providing a smooth, hard surface that allows the gold leaf to be burnished to a brilliant lustre. 

The preparation of all of the recipes used in water gilding are quite precise including that used to make gesso. One very important consideration is the strength of the RSG formula which is a 10% solution: 9 parts water to 1 part dry RSG, either in pebble or granular form. If the RSG solution is prepared too strong there is risk in developing crack mechanisms in the gesso layer. Likewise, if the RSG solution is too weak, one faces the possibility of delamination of gesso from the wood substrate.

Numerous layers of warm gesso are painted, stippled, or sprayed onto the wood surface. Each layer is allowed to dry only long enough so the application of the next layer does not disturb the previous layer. Anywhere from 5-20 coats may be applied, depending in part upon the object and the desired effect. The concept, which dates back to the early Egyptians, is that the wood is intended to appear as solid gold, an effect created largely by the use of gesso as a ground for gilding.

There are a variety of approaches used throughout the world in the successful preparation of gesso and although recipes and methods may seem at first glance to differ, the basic principles of glue strength and the ratios of RSG to Whiting are quite similar when analyzed. Logically, they would ultimately need to be since the relationship between the binder and the particles of calcium carbonate are subject to the same chemical principles.

Monday, July 11, 2016

We Get Questions....

We get questions about gilding quite often. Many from artists,craftsman and designers around the globe.

It's our intention to post some of those questions -and answers!- right here on the blog so that we may reach as many people as possible.

Do you have a question about gilding? Please feel free to respond with any of your own and we'll make every effort to answer you in a timely manner.  We hope you'll find the information helpful and this blog a valuable resource.

This one is from Dom in Australia:

Q:What glue or adhesive would be best to gild paper? 

A: Concerning gilding paper, the traditional method for manuscript illumination is a method of water gilding using gesso sottile and clay bole. The bole contains a binder such as glair which is beaten egg white. Other binders have been used for many years for use on paper including gum arabic and gum tragacanth which is a gum derived from a plant in the Middle East, mainly Iran.

This form of gilding, however, is a very specialized process. So, for your purposes you could just experiment with making glair by beating an egg white with a little bit of distilled water (enough to fill one half of an eggshell); let it sit overnight and drain off the froth the next day. Dilute the egg a little more till it flows freely from the brush. Apply one coat to the paper and let it dry to seal it, then add another coat and apply the leaf. You can read about this method in the 15th Century Florentine treatise written by Cennino d'Andrea Cennini: Il Libro Dell'Arte (The Craftsman's Handbook).

A modern day product, aptly called Paper Size, is simple to use and provides a bright burnish. It's manufactured by Kolnar Glanz in Germany and distributed by Sepp Leaf Products in New York. 

Saturday, July 9, 2016

A Florentine Perspective in New York City...Come Take a Class!

Join Us in NY in September!
Gilder's gesso, made from calcium carbonate and rabbit skin glue, forms the ground for traditional water gilding and in turn allows the applied gold leaf to be burnished to a lustrous glow. As centuries pass, the movement of the gessoed wood and environmental factors cause a distinct crackling in the gesso layer adding further aesthetic complexity as can be seen on such objects as 13th-15th C gilded panel paintings of Italy as can be seen in the Accademia and Uffizi Galleries of Florence.

During this five day intensive workshop students will be taken through each step of the crackled gesso traditional water gilding process, from sizing the wood and preparing the crackle gesso to laying genuine 23k gold leaf and toning. A book of 23k gold leaf and a raw wood panel will be provided for students to gild and take home. 

All materials and use of gilding tools are available for class use. For those interested in acquiring their own gilder’s tools, a specially selected Traditional Water Gilding Kit is available. Visit at for more details. Use promo Code GSclass2016 for a student discount.

Tuesday, July 5, 2016

Superyacht Invictus

Superyacht, a term often used now for a commercially operated luxury yacht where one may find marble floors, spiral staircases - or, if you prefer - an elevator. And in this case, 900 feet of 23kt traditionally water gilded moulding.  

2013 saw the completion of Invictus, a yacht built by Delta Marine in Seattle who contracted me to gild the interior of the Executive Office on the top floor of this magnificent 215 foot ship.

When I first met with Delta and the Diane Johnson Design team, we reviewed the plans for gilded mouldings that would later be fitted into routed grooves (see photo below) along with cove and floorboard mouldings that would combine gilding and black catalyzed varnish. 

Superyacht Invictus
The presentation of various samples of gold leaf gilded mouldings resulted in a choice for water gilding due to its elegance and ability to balance the requirements of a hint of brilliancy against an aged appearance with a rubbed leaf over a dark, earth-red ground. The hermetically sealed design of the ship, of which I was informed is better than one's home, would provide a suitable environment for the gesso-based gilding.

The final design plan was to use water gilded 23kt gold leaf, burnished over a custom-mixed dark red bole consisting of 50/50 German Red and Black clay. The leaf would be rubbed to expose the dark red bole and then toned with an umber-tinted Ruby shellac.

As for challenges, there are always difficulties with a large scale project that need to be confronted and resolved. In this case one of the larger issues was that the mouldings to be fitted into the wall panelings measured only a quarter inch wide and were joined at the mitres like picture frames so the mitre cuts wouldn't show. Unfortunately, once hydrated, the frames bowed in the middle causing some of the corners to pop open - I would sometimes actually hear them snap from across the room! - so the handling of these delicate mouldings proved very difficult, especially during burnishing. As the wall panelings were already meticulously painted the gilding needed to be done separately and the mouldings inserted. 

Finished Moulding 
Applying weights on the corners of the frames after any hydrating helped stabilize them and after many hours all the various sized frames were finally gilded, toned, and installed successfully.

One of the aesthetic challenges was that some of the gilding was accomplished in the studio, some onsite in the manufacturers's workspace - the size of a small airplane hangar - and also onsite on the yacht itself in a separate hangar amongst the wiring, cables, woodworking, and painting of the yacht builders. The goal was to maintain a consistent antique color tone on all 900 feet of moulding, executed under three separate lighting conditions while also envisioning how the appearance may change once the ship was launched where the lighting would change once again under natural conditions. The only true approach to this is to maintain awareness, make sure the toning recipe and application is consistent, and to not go too dark on the tone - it's always easier to make something a bit darker later than lighter.

In the end, the look of the water gilded gold leaf set against the deep, dark black elegance of the varnished walls and cabinetry was quite stunning. Several studio assistants were on hand to contribute their skills throughout this year long project: Madeline, Heather, Alyssa, and with a special thank you to Swedish Gilder and Restorer Malin Isaksson who flew many miles to be involved and lend her assistance. (To view some of Malin's work visit the website at the Stockholm Furniture Fair.)