Zinc Oxide – Reviewing the Research

Titanium-Zinc cracks easily (Photo from juspaint.org)

An expected and alarming article about the hazards of using zinc oxide in painting. Research shows that “combinations with a wide number of other pigments, including Titanium White, does not appear to mitigate zinc’s brittleness”, and that “lowering the percentage of zinc to even these levels* did not seem to make the blends any safer to use” (* previously the manufacterer had reduced it to 2%, but further review showed the need to completely removing zinc oxide).



“Substitutes” for Cadmium Yellow

Cadmium Yellow Medium (Maimeri Puro)

There are concerns that cadmium yellows (PY 35, or cadmium sulphite) may fade over time, as has been observed in several paintings, although this pigment is rated as having excellent lightfastness (or 8;8;8 at BWS – Blue Wool Scale). There are reports of Van Gogh, Matisse and Munch works where the cadmium yellow turned into a milky-gray compound. Researchers have found that one variety of cadmium yellow becomes cadmium sulfate when it is exposed to excessive dampness and light, over decades. Some say this is problem that affects only the cadmium yellows produced before 1920, as the manufacturing process has changed since then. So, actual paints of such pigment would be stable. But, besides, there are the safety issues related to cadmium pigments.  These questions may lead one to look for a substitute for cadmium yellow.

Unfortunately, there isn’t yet an ideal replacement. Others yellows usually fail in offering equivalent opacity and covering power.

Commonly, yellow pigments used as “substitutes” for PY 35 are: PY 74, PY 73 and PY 65. All of these three are labeled as being of low hazard.

PY 74, a “hansa” (or “azo”, or “arylide”) yellow, may be not entirely reliable: it’s rated as having just a good lightfastess (or, sometimes, a 7;6;5 at BWS).

PY 73 e PY 65 are the “azos” with better lightfastness. PY 73 ranges from reddish to greenish yellow. It’s not opaque as a cadmium. PY 65 tends to present a more reddish tone, and may be a bit more transparent than PY 73. I’ve tested Winsor Artist’s Yellow Deep, produced with PY 65, and it’s really a bright reddish yellow, nearly an orange, as can be seen in the photo. It’s nicely saturated.

Others oil paints that are produced with this pigment are Lefranc & Bourgeois Chrome Yellow Deep Hue and Williamsburg Permanent Yellow Deep.

Above: Maimeri Puro Cadmium Yellow Medium (PY 35) Below: Winsor Artists’ Yellow Deep (PY 65)

Drawing of the day

Grey papers are great for portraits, because light areas can be highlighted with white pencil. I had a hard time trying to find a toned grey paper, and I’m surprised by the quality of this “Canson Color”. Unfortunately, I’ve just found it in size A4. It’s 180g/m2, and it has a fine grain, good enough for drawing.

For this self-portrait I used Bruynzeel and Staedtler graphite pencils. So far, Staedtler softer grades are the darkest I’ve found. The white pencil used in this drawing was Koh-I-Noor Hardtmuth “Gioconda” White Coal. By the way, Koh-I-Noor produce a lovely black charcoal pencil (from this series “Gioconda”).

Drawing stages

Some people like to start a drawing making first the great masses of values. I prefer to draw the main lines, visualizing the features and proportions of the face before working on the fine details. The white highlights come last. To avoid smudging the paper with my hand, while drawing, I like to place a tracing paper under the hand.

Pencil drawing self-portrait


Preparing a canvas for oil (or acrylic) painting

I got a little help from my studio cat while making this canvas.

Learning how to make your own canvas is really useful, because often store bought canvas don’t seem to be well prepared for painting. Sometimes they have a sparse coat of gesso, or the fabric is too thin. This can compromise the visual final result, or the painting conservation over time. Most importantly: oil paint shouldn’t be applied directly on the fabric, because eventually it will damage the fibers.

Materials needed to prepare a canvas: fabric (usually cotton or linen), a brush, PVA glue, acrylic gesso, a sandpaper. Besides these, a wooden frame and a stapler, if you want to stretch the fabric before to prepare it.

The fabric may be prepared after it was stretched over a wood frame (what I prefer and recommend) or no. If you are using a wood frame, it’s advisable that the laths have a rounded edge, so the frame wouldn’t rip the cloth where it folds (see in the picture). I’m using here an already built wooden frame, from a canvas previously used for a study. In case I make the frame, I prefer to ask a carpenter to saw the wood, so I’m sure it’s cut in perfectly 45 degrees angle.

Red arrow: rounded edge (for the side in touch with the fabric); blue arrow: sharp edge (canvas backside)

There are a couple of ways to prepare the fabric. This one, I think is the most practical and useful I’ve learned.

First of all, one needs to choose the fabric. The most used are linen and cotton. There are some others, like polyester and jute. Linen has been used for a longer time. It’s quite more expensive than cotton, and stiffer to stretch. Usually, it offers a delicate woof. Some people argue that linen lasts longer than cotton, because cotton absorbs more moisture. But the better durability of linen is not well proven. From my experience, linen is also somewhat harder to find.

Cut the fabric at least one inch larger than the frame, to fold the excess in each side.

The fabric texture may be coarse  or more regular and even. This is a matter of personal preference, and it depends greatly upon the final result one wants in the painting. Usually, a delicate surface is desired for realistic paintings. Also, differents textures present differents “feels” for the brushwork. Still talking about the fabric: it’s recommended that the fabric be raw, not dyed. The raw cloth usually has a beige ir brownish tone. Fabrics may be composed by a hundred percent type of fiber, or they may have synthetic fibers on it – for example, 20% polyester and 80% cotton; but it’s not known for sure if this is good, in terms of durability (distinct fibers may behave in an unequal way under climate variations).

A heavy stapler is needed to fasten the fabric to the frame

A heavy stapler is needed to fasten the fabric to the frame. It’s better to place the first staple of each side in the middle. After fastening one side, do the same with the opposite side.

A stretched fabric of raw cotton, over the frame.

SIZING – If the cloth is stretched on a frame, ensure that it’s not too tight, because, after the glue is applied, the fabric shrinks, so this will warp the wood.

This is the step when we fill the gaps in the fabric. The simpler way to do this is by applying a layer of PVA (polyvinyl acetate) glue. This process isolates the fabric from the paint, thus protecting it. If the canvas wasn’t well prepared at this stage, over time the fibers will rot, and also stains of oil may emerge on the back of the canvas.

This glue layer also acts by decreasing the flexibility of the cloth, locking its threads, and avoiding them to expand or contract (what happens due to moisture  in the surroundings).

In the old days (and some people still do it) rabbit skin glue was used for sizing. But, besides PVA glue being more convenient, I prefer to use a non-animal origin product. There are also some concerns that rabbit skin glue has conservation issues.

There are other products that can be used for sizing, like some types of acrylic foundations (be sure that the label specifies this purpose).

You may need to add a bit of water to the PVA glue, so it will be easier to spread. But don’t dilute the glue too much, or it will lose its function.

Apply the glue generously with a large brush, until the fabric is soaked in glue. Don’t forget to apply it on the sides. I like to apply the glue also on the back of the canvas, the improve the protection from moisture.

Applying PVA glue. After the glue is dry, it will be transparent.

I’m showing this process in which glue is applied, and, after this,, the gesso comes. But some people use a single mixture that serves both for sizing and gessoing, at the same time. This mixture usually is made up with PVA glue and latex paint. But there is a risk that wall paint won’t perform well in terms of lighfastness.

PVa glue dries fast, but it’s safer to wait for some hours before jumping to the next step, so we’ll be sure that it’s really dry.

PRIMING – It consists in applying layers of “gesso”, after sizing. The “gesso” that we use today (acrylic gesso) is actually not authentic gesso. Before acrylic gesso was available, a mixture of rabbit skin glue (or another binder), chalk and white pigment was used for priming. Over time, emulsions of acrylic resins have inherited the name “gesso”, as they substitute its function. Usually, the acrylic gesso that we find readily to use at stores are suitable to prepare the canvas for both oil and acrylic paints (but specific oil based primers shouldn’t be used to prepare a canvas for acrylic painting).

The priming creates a coat ready to accept the paint. It also changes the absorbency of the canvas, its texture and color (if you add a tone to the gesso). Most importantly, the priming improves oil painting adherence to the surface.

The gesso should be applied in layers, at least two of them. A more even surface may be obtained with more layers. The acrylic gesso may be thinned with up to 15% water. The first layer consumes more gesso. As the surface becomes less absorbent, the next layers consume gradually less gesso. I spent about 300 to 350 mL of acrylic gesso for printing 10 to 12 square feet of canvas (I applied 3 coats of gesso).

Applying the first coat of gesso

Use a large brush or a paint roller to apply the gesso, and don’t forget the sides of the canvas. A brush for wall painting tends to drop a few bristles, specially at the beginning, so you may need a tweezer to remove them, and any other lint, while the gesso is still wet. As this process quickly wear out the brush, it’s not worth to use a fancy (and quite more expensive) oil painting brush.

The acrylic gesso dries fast, what can be checked touching the surface (it’s cold if it’s not dry yet). Usually, in up two hours it’s dry, but this may vary with the weather. The second layer should be applied in a perpendicular direction of the first, and so on.

A canvas after the printing with 3 coats of gesso

After the last coat is dry, the canvas should be scuffed. A sandpaper of 320, or with a thinner grit, is fine to sand the canvas. The grit depends upon the final result one wants in the surface. After this, your canvas is ready.

Scuffing the surface, after the last gesso coat is dry, with a 320 grid sandpaper.
Finished cotton canvas, ready for painting

Alternatives to Cadmium – Part I – Reds


Cadmium provides brilliants shades of yellows, orange and red paints. Before of cadmium-based pigments, painters hadn’t such permanent reds. Cadmium colours are also vibrants, with a high chroma, and have a strong tinting power.

Unfortunately, cadmium is a toxic metal. With proper care the artist can avoid contact while handling materials, but a safer option would be to choose other pigments. Cadmium is a cumulative toxin, that can be absorbed through inhalation of its dust (a risk to whom make their own paints), by ingestion or through skin. Even that dermal absorption is not a significant route of cadmium entry, it happens. And, even very low levels of this metal may have adverse effects in our body (especially in the kidneys).

Cadmium red is cadmium sulfoselenide, and as a pigment is known as PR 108.

A “perfect substitute” would have all the same properties of the pigment, what, at least presently, is not possible. But there are some good alternatives.

So, for the cadmium red (PR 108), I’ll highlight these: PR 254, PR 255, PR 112, PR 170, PR 149. For what I’ve seen so far the first two seems to be better as “substitutes”, due to  its lightfastness (if this is a main concern).

PR 254 and PR 255:  Pyrrole reds. Excelent lightfastness (888 at the BWS). They have high chroma, and are highly staining. The PR 255 is slightly yellower than the PR 254. They are less opaques than the cadmium reds. Examples – PR 254: Maimeri Puro Sandal Red, Rembrandt Permanent Red Deep. PR 255: Blockx Pyrrolo Red, Rembrandt Permanent Red Medium.

Top row – real cadmium: Rembrandt Cadmium Red Medium and Maimeri Puro Cadmium Red Deep Bottom row – an alternative (PR 254): Winsor and Newton Artists’ Bright Red. (*pure colors and mixed with 50% titanium white)

PR 112: Naphtol red. It’s a intense bright yellowish red. Heavily staining. Less opaque than cadmium (but I think that it is a bit more opaque than the pyrroles – to be confirmed). It has been rated as having excellent lightfastness under ASTM testing, but other testing methods have demonstrated some tendancy for the color to fade with exposure to strong UV light, and its is BWS 7-8;6-7;5. M Graham Naphtol Red, for example, has its lightfastness labeled as “Lightfast Rating Very Good – LF II”. Examples: Williamsburg Fanchon Red (ASTM II), Old Holland Scheveningen Red Medium.

PR 170: A Napthtol red. Its lightfastness may not be reliable (ASTM I-III). I found this interesting info on Dickblick “The lightfastness and weatherfastness of Pigment PR170 varies, depending on the application and the crystaline form. The opaque form (F3RK) has very good lightfastness, and is more weather resistant.” Sennelier Cadmium Red Medium Hue is rated as ASTM II (good lightfastness). Examples: Sennelier Cadmium Medium Hue, Michael Harding Scarlet Lake.

PR 149: Perylene red. It has good lightfastness and permanence. It may darkens (with exposure to sunlight). But Winsor and Newton Artists’ Winsor Red Deep is labeled as “Lightfastness (ASTM) I”. It’s a semitransparent color. Examples: Michael Harding Crimson Lake, Rembrandt Scarlet, Holbein Artists’ Perylene Red.

Although descriptions of pigments technical features are hightly useful, they can’t replace the experience of using a particular pigment or oil paint.

UPDATE: I’ve bought a tube of Rembrandt “Permanent Red Medium” (#377), made with PR255. The color is pretty much similar to the Cadmium Red Medium of the same brand, maybe slightly (really slightly) warmer. The great differences of this pyrrole to this cadmium: its transparency and weaker tinting strength, compared with a cadmium (although it has a good tinting strengh).

Rembrandt Permanent Red Medium (#377), made with PR255

Time-Lapse Videos – Small Paintings

I started this week to film small paintings, in order to make timelapse videos. I’ve filmed two so far. The first one is full of mistakes, the second is a bit better, but I really need to get improvement in lightning, to avoid all the glare of the wet paint. Interesting, being worried about filming made me easy going about these small works, what I though really nice. No previous drawing, no overthinking.

Pure Titanium White Oil Paints

Pure zinc oxide oil paints: right out of the tube, Talens Rembrandt Zinc White No 104 at left (ground in safflower oil, noticeable whiter) and Michael Harding’s at right (ground in linseed oil, so, a bit yellowish) – from tubes I bought and, unfortunately, don’t use anymore

A paper published in 2013* raised (even before its publication) a worrisome question about conservation of paintings made with zinc white. It has been demonstrated that paints that contain zinc oxide will become brittle, in relatively short periods of time (as little as three years!). Also, further damage occurs by delamination of adjacent layers of painting made with other pigments. The authors did not mention the amount of zinc oxide in each studied paint, but one can wonder that even small proportions of this compound may cause disastrous effects in an artwork.

The scientists who demonstrated the long term problems with zinc oxide paints also noted an outstanding durability and toughness of the paint films made with lead carbonate. Unfortunately, the health issues associated with lead are, of course, a major factor to avoid its use (I’d be afraid to use it, even with great caution).

After knowing how potencially hazardous zinc oxide can be, I don’t use it anymore. Now, where we have to be careful: zinc oxide is present in several white paints, even if it isn’t clearly stated, as in many “Titanium White” oil paints and even mixed in a few other colors. Zinc oxide (PW4) is blended to titanium white (PW6) in oil paints to give them a less spongy texture. Also, zinc oxide is less opaque, and have a weaker tinting strenght, features that sometimes can be desirable. Recently, I made a list of whites that allegedly don’t contain zinc oxide:


  • BlockX
  • Blue Ridge
  • Daniel Smith
  • Gamblin Artist’s
  • Holbein Artists’ and Holbein Vernét
  • Lukas 1862
  • Maimeri Puro
  • Michael Harding’s (Titanium White No 1)
  • Old Holland
  • Pébéo Huile D’Art
  • Vasari
  • Williamsburg
  • D’Arte Cor (Semi-Profesional)

– This list was made in May 2017, so it may undergo changes or become outdated, if the manufacturer alters the composition, so, I’d recommend to always read the label
– It’s not meant to be a thorough list, just an useful one, as there are some important brands missing (although I’ve checked a lot of them)

*Source: Mecklenburg, Tumosa, Vicenzi (2013). “The Influence of Pigments and Ion Migration on the Durability of Drying Oil and Alkyd Paints” Available online: https://repository.si.edu/bitstream/handle/10088/20490/12.Mecklenburg.SCMC3.Mecklenburg.Web.pdf?sequence=1