Rabbit Skin Glue is a traditional glue used as an ingredient in the preparation of genuine gesso and half-chalk ground; as a sealant (size) on canvas and wood panels before applying traditional gesso or an oil ground or to be painted on directly with oil paint; as the binder when making distemper paint; and as a glue in some book making and other fine craft. Rabbit skin glue is made by rendering the gelatine from animals, usually not rabbits, and the name designates a particular concentration of glue; hide glue is a name given to the same product at a different concentration. There are a few myths and some confusion about the use of RSG and there are some modern alternatives.
Why we Size
When preparing a canvas or wood panel that you plan to coat with an oil ground or genuine gesso, the canvas or panel needs to be sized first. This is a transparent layer that seals the surface and in the case of canvas (both cotton and linen) it tightens and stiffens the fabric. Canvas needs to be sealed from the effects of the drying oils in oil paint and oil grounds because over time the oil will degrade the cloth fibres causing the canvas to darken and become brittle. This is the premature ‘rotting’ of the canvas you hear about. Wood panels do not need to be sealed from oil but sizing gives a better surface for oil grounds or genuine gesso grounds to sit on by evening out the absorbency of the wood which would otherwise have different absorbencies between the grain lines and the wood between them. Sealing the wood also prevents moisture from drawing up colour, acids, glues, etc. from the wood into your gesso. This sizing can be done with an acrylic polymer (see the bottom of this article) or with rabbit skin glue which is often abbreviated as RSG.
Introduction to RSG
Rabbit skin glue (RSG) comes as a dry product that you need to make up with water. It can come in fine or coarse granules or little cubes – in a plastic-lined paper bag or plastic container. Because it is affected by water it needs to be stored somewhere dry, and then it can be safely kept for many years. It doesn’t take as much of the dried glue as you might think because you add a lot of water to make it and it expands enormously. You also apply it very thinly. You make it up fresh as you need it and because it must be heated gently you use a double-boiler (bain marie) process. Because I do not have a hotplate in my studio, but of course I have access to an electric kettle for tea, I use a very simple method using 2 plastic buckets and a kettle of boiling water. You then apply it warm or make gesso with it warm. It is a jelly when cold and a thin liquid when warm. We also stock ready-prepared RSG which is a bit more convenient, though it still needs to be melted and applied warm, and it is not as economical as hydrating the dried granules yourself.
The Amount of Water to Add to the Glue Granules
Glue strengths can vary depending on format and supplier. You can tell the concentration of the glue by how much it gels when it has cooled. For sizing rigid surfaces or making gesso, use 1 part granules to 12 parts water – when cooled it should be a firm jelly. For sizing canvas some experts use the same concentration, while some recommend a thinner consistency of 1 part granules to 20 parts water – when cooled it should be a soft jelly which is easy to stir to an applesauce consistency, and still other experts recommend a thicker solution of 1 part granules to 8 parts water.
The consistency changes as it cools so you can control the viscosity as you apply it by using it at its warmest when it will be the most fluid or by letting it start to cool and thicken. If you use a higher concentration of glue you will need to apply fewer coats. If you use the thinner concentration it will help you get the thin layers you want but you will need to apply more layers to make sure canvas is sealed enough to prevent oil strike-through.
Because there is some wiggle room in the ratio you do not need to be super accurate and can make your glue using volumetric measurements – if you are using perhaps an old yogurt pot then 1/4 pot of granules and 3 pots of water = 12:1. But measuring by weight will always be more accurate because the size of the granules can change the amount of glue in a volume. A kitchen or postal scale works well. 12:1 requires 35g of dry glue granules per litre of water. 20:1 requires 20g of granules per litre of water. And if you switch to a different brand or format of dry glue then you may get different results then you had been used to, because the new dry glue might be weaker or stronger. For panels I personally use 12:1 and I measure by volume.
The Yield or How Much to Make
You may not need to make as much as you first think, as you apply the RSG thinly and you can’t store the leftovers for very long, even in the fridge. Making up a litre should allow you to size eight small panels (20x25cm) and use the rest to make gesso for them the next day. You will use about 1/3 to size and then the next day rewarm the 2/3 left to make up the gesso that you will need. To make the litre of RSG at a concentration of 12:1 requires 1 litre of water and 35g of dry glue granules.
The Preparation Method
To make up some RSG you will need two similar sized containers that can withstand boiling water and one needs to fit inside the other – I use empty Golden Gel 4-litre buckets. Below we show a 2.5 litre bucket in a 5 litre bucket. If you have a hot plate you can put a pudding basin in a saucepan.
Put 8-20 parts cold tap water and 1 part RSG pellets in a container and cover and leave until the glue particles have swollen and increased greatly in size, no need to refrigerate. For large particles of glue like the cube format this will be overnight or longer, for the fine granules it could take just a few hours.
The next day, boil the kettle, pour a few inches of hot water in the other container and set the bucket with the cold water and soaked glue pellets into the hot water bucket. You don’t want to get the glue too hot or it will be damaged, but the cold water inside and the boiled water outside should be just right. Because my studio is cold the bucket of soaked rsg and water is quite cold so the boiled kettle water cools quickly enough to not be too hot. If you are working in warmer temperatures perhaps hot tap water might be enough. The same is true for gelled RSG stored in the fridge, it comes out quite cold so the boiling water in the bain marie should cool fast enough to not damage the glue. You want to warm it not cook it. If you are using a thermometer, keep the temperature below 70C. Stir and it will slowly melt into a liquid glue with the consistency of milk. I have heard that you can filter the glue through an old pair of tights to eliminate contaminants but I have never needed to do this.
When it cools it will be a jelly. You can store it for some time in the refrigerator and re-melt it, but it is best used as soon as it is ready, so try to make up only what you need. I have not stored it for longer than 2 weeks and I have read that most people recommend 1 week.
We also sell ready-prepared rabbit skin glue that is already a jelly and has been strained/filtered and just needs to be melted gently in a bain marie set-up (just like before- do not get it too hot). For some reason this kind doesn’t need refrigeration, it must have a preservative. It is convenient but since you don’t add 12 parts water to it like you do with the dried RSG, it is not as economical.
Preparation step by step in photos
Fresh Rabbit Skin Glue does not smell bad
Years ago, when I first used it, I was prepared for a bad odour because I had heard that people avoid RSG because it smells foul. But mine had almost no smell. I have since smelled spoiled RSG left in a cupboard in a classroom that smelled terrible, like a decomposing mouse. I think the smelly stuff is remembered from art school where stuff gets left over and reused and not refrigerated in which case it will spoil. It should only smell bad when it has spoiled. Do not use old, stinky or mouldy glue.
Applying RSG to Panels or Canvas
Apply the glue size thinly, evenly, quickly and in one direction while warm. Let it become touch dry between layers (less than an hour). Then apply the following layer in a crosswise direction. All layers must be thin because a thick layer of rabbit skin glue is more likely to crack later, even on panel.
To size a panel apply two layers while very warm and flowing. I use it directly from the bain marie set-up – brushing it onto wood panels held at an angle with the draining corner over the bucket for the excess to run back in. Some people mix in a small amount of the whiting that you will use to make your gesso, which allows you to see a milky coating evenly on your surface, so no area is missed.
To size cotton canvas apply 2-3 layers, while a bit cooler but still warm, rewarm if necessary to keep the glue fluid. For linen with its more open weave you may wish to apply it with a brush or large palette knife when it is even a bit cooler, starting to thicken, to better fill the gaps in the weave. There is no need to add whiting for applying the size to canvas, if you wish it to remain clear, you just need to be careful to coat the whole canvas.
While you are working with it, as it cools it gels and you just need to change the cooled hot water for fresh hot water to re-melt the glue. Since the glue is no longer as cold as when it started, be careful with getting the bath water too hot; you can re-melt is as often as you like so long as it doesn’t get too hot.
On canvas the RSG should cause the fabric to shrink and this may be so pronounced as to warp your stretcher bars, especially with linen. For this reason some artists staple the canvas evenly to a wall in their studio to size it and then stretch it on stretcher bars and apply the ground. Or use tacks to stretch it temporarily for sizing and then re-stretch it for applying the ground. It is much easier to stretch linen evenly on your bars if it has already been sized, because it is stiff enough to not be wavy and stretchy. Which is why we stock Glue-Sized Linen, so you just need to stretch it and apply a final coat of RSG or a ground. Think of it as semi-stiffened or partially-prepared linen.
The now sized canvas or panel needs to dry flat for at least 12 hours – and let it dry naturally, don’t use a drier to speed up the drying. If your panel bends because it is thin or not cradled you may want to paint RSG on the back to flatten it out.
Painting on RSG-sized Canvas
If you do not wish to apply a ground, you can paint with oils straight onto the RSG-sized surface. Many artists like the look of a clear sized linen surface and the surface feel of painting directly onto the RSG sized canvas, so they do not apply a ground. To test if you have enough RSG on the canvas to seal it properly, check the back of the canvas for any seepage or strike-through of the oil paint. If you paint with very fluid oils that are thinned with a lot of solvent you may find that the RSG will not be able to withstand the penetration. Do not paint with acrylics or put acrylic primers on RSG as they will not stick well.
Applying a Genuine Gesso Ground to the Sized Panel
Genuine gesso is a mixture of glue and chalk and like the size it is applied warm. It is used for, among other things, making panels for egg tempera painting because acrylic primers are not absorbent enough and the paint lifts off as you begin layering it. It is also an absorbent enough surface for encaustic painting. The ultra-smooth, soft, very white and absorbent surface is also preferred by some oil painters, especially if they make meticulous renderings. Genuine gesso is only used on panels because it is not flexible, and so it will crack if used on stretched canvas.
There is an efficiency to making many at once. It doesn’t take much more time to size and gesso eight panels than one. For instance, as you are applying size to the eighth panel the first is probably dry enough to get the second layer of size. Then when applying the five or more coats of gesso, you only wait for a coat to become matt before applying the next, as all coats must be applied in one session otherwise the coats will not bond together. So again, by the time that you have coated the eighth the first is probably ready for the next coat and in this way you can do a series of eight in the same time as one.
Making Genuine Gesso
True gesso or traditional gesso (as opposed to acrylic primer which is often called gesso) is made from warm 12:1 RSG and an inert white pigment. This pigment can be called a number of things: gypsum, chalk, marble dust, or whiting. (The word gesso comes from the word gypsum which is why it is pronounced like “jesso”.) You can substitute up to 20% of the inert white pigment with titanium white pigment if you want a bright white surface.
Measure the amount of RSG you have and put it back in your double boiler. Measure 1.5 times the volume of inert white pigment, at Jackson’s we call it whiting. Slowly slip the powder into the liquid without stirring or creating air bubbles, let it form a mound and let it settle and soak for 10 minutes. Then gently stir it with a wet brush, trying to create no bubbles.
Apply the gesso to the sized panel in one direction back and forth, rotating the panel to do each subsequent coat in the crosswise direction to the last. When the shine has left apply the next layer, all 5-10 layers need to be applied the same day for the layers to bond. If there are any cracks, you are not waiting long enough, but the next layer should fill the cracks. If you are getting pinholes that is from air bubbles and you should tap you bucket of gesso sharply on the table to cause the bubbles to rise to the surface and then let the gesso settle for 30 minutes before continuing. You can burnish bubbles out by rubbing with a wet muslin cloth, wet smooth block of wood or your wet finger. The layers are transparent while wet and until you have built up some coats.
Let your panel dry for three days and then smooth it. Fine sandpaper or a sanding sponge are best used wet because the dust is dangerous to breathe. As well as the face, sand the sides to bevel them a bit. If you need a very absorbent surface use the panel as it is. If you wish to reduce the absorbency for oil paints perhaps, then you can add a final coat of RSG.
A similar substance for making painting panels is chalk ground, which has a lower percentage of whiting, 1:1. Half chalk ground is chalk ground with linseed stand oil added. Both of these are generally mixed on a glass palette with a painting knife, working the powder into the liquid in a similar manner to making paint. These can be applied to stretched canvas because the oil content or the higher glue content allows them to be flexible enough.
Applying an Oil Ground to the RSG-Sized Canvas or Panel
An oil ground is composed of a drying oil (usually linseed oil), an alkyd resin or both, with an inert white pigment for tooth and usually titanium white pigment for opacity. It is similar to a layer of oil paint, so needs to dry or cure before painting on. Read the instructions on the container and prepare your canvas or panel ahead of time and allow it to cure for the recommended time. The surface will yellow because of the linseed oil but if you cover the whole surface with paint this will not show. The surface in not very absorbent so the paint slips around and the wet paint can be wiped away easily. Many oil painters find it a superb surface much preferable to an acrylic ground.
The Drawback of RSG
There is a conservation drawback to using RSG. It is hygroscopic, meaning it absorbs water from the air over time, causing the glue to swell or shrink as humidity levels change and the repeated flexing of the surface underneath the oil paint causes the oil paint layer to crack. RSG is considered to be a major cause of cracking in oil paintings by most modern conservators. Although it is traditional and has been around for many years, museums have had to work hard conserving some paintings.
The most damage occurs when there are rapid and wide fluctuations in relative humidity, more so than very slow or minor changes. If the relative humidity gets above 85% then the RSG has no rigidity at all so contributes no support and the canvas is free to shrink so the paint can do little but crack or delaminate. But in most climates that is rare. It is most problematic with very old paintings where the oil paint has become very brittle over time.
Because of this changeable, reactive quality of the RSG some people choose instead to use acrylic size on canvas and panels to seal underneath their oil ground for oil painting. But it is still necessary to use RSG as an ingredient in genuine gesso for egg tempera painting. Additionally there are reports that canvas prepared with RSG becomes brittle, but so does oil paint if painted on any stretched canvas, so if you are worried about the cracking of oil paint, conservators recommend only painting on a non-flexible surface such as a wood panel or canvas attached to a wood panel, and never on a stretched canvas.
To ameliorate the problem with RSG apply it as thinly as you can get away with while still accomplishing your purpose; the less you have on your surface the less it can swell and shrink. And of course, storing your work in a less changeable environment will help. There are modern synthetic alternatives, though the surface does not have the same look or feel as RSG, which is often described as sparkling on the surface of the canvas and allowing oil paint to sink into the surface. And they don’t tighten the fabric like the RSG does. In fact, modern sizing alternatives often cause the canvas to slacken.
Synthetic Alternatives to Rabbit Skin Glue
In addition to problems of RSG not being perfectly archival some artists are concerned because it is an animal product. If this is a concern you may wish to know that although it is made by rendering the gelatine from animals, they are not usually rabbits, the name designates a particular concentration of glue; hide glue is a name given to the same product at a different concentration. RSG is a by-product of the meat market and no animals are killed just for the glue.
For either of these reasons you may wish to use a modern synthetic alternative to hide glue, though they will not work in all situations. Although acrylic sizes are designed for use with acrylic primers and acrylic paints they can be used for sizing canvas before applying an oil ground for oil painting. You can apply one or two coats of GAC 100 or a similar polymer medium directly to the raw canvas, worked well into the weave. If you wish for a stiffer feel use GAC 400 for the first coat and GAC 100 for the second coat. Golden Acrylic’s latest research seems to point to GAC 200 working like both GAC 400 and GAC 100 so you just need two coats of that on it own. Since they are acrylic polymer, they are only very slightly hygroscopic, which makes for a much more stable surface over time. Lascaux make a great acrylic size. Ara make a great acrylic and casein size. If you want a clear size to allow the colour of a linen canvas to show then a polymer gloss medium would be a good choice – a matt medium will leave a cloudy surface as will many clear primers/gessos. And the feel of painting on the plastic surface is very different from painting on the RSG surface.
There are also PVA sizes but I have read that a reputable painter and materials researcher does not recommend PVA size as it is prone to deterioration. But that may be because there are over 50 different types of formulations of PVA (Polyvinyl Acetate) and only a few are of a good enough quality to make permanent paintings because they have low acidity, retain flexibility, and have low colour change. Look for pH neutral, sometimes called acid-free, PVA. PVA not made specifically for artists will deteriorate and is to be avoided. Gamblin make an artist-quality PVA size.
Acrylic primer is easier and quicker to use than RSG and true gesso, with more predictable results each time. It is both a size and a ground in one. However, these modern replacements do not stiffen and tighten the canvas as well as rabbit skin glue does, in fact they tend to loosen the fabric so it may need to be re-stretched after priming, so some artists still prefer to use RSG.
RSG and Related Materials at Jackson’s
- Rabbit skin glue
- Oil primer/ground
- Modern synthetic sizes
- Wooden panels
- Unprimed (raw) canvas by the meter
- Clear glue-sized canvas
- Icon soft mottler brushes
- Plastic paint buckets
This post was updated on 21st June 2021.