Cracked paint

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JanetK49 wrote
on 12 Mar 2010 2:31 PM

wmmccoy,

wmmccoy,

Thank you many times over for looking at the painting in question and giving me some solid advice on how to fix it.  I've just been watching the cracks get worse these past few years (they weren't noticeable at all for the first 20 or so) and wondering what to do about them.  I have a couple of questions though that maybe you have an opinion on (or maybe not).

First, I like the idea of the fill, repaint and varnish, but since the cracks have been growing in the past few years as I said, do you think that I will have to go back and fill, repaint and revarnish, let's say, in another 10 years?  In other words, do you think they will continue to grow?

Second, I haven't used Liquid Alkyd medium before.  Any particular thing I should know about it before I do?  I'm using strictly water mixable oils now and painting alla prima for the most part so haven't used any additives in a long time.

Thank you again for your clear and concise steps for this repair.  I appreciate your advice a great deal as the painting has a lot of sentimental value to me.

JanetK49

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wmmccoy wrote
on 12 Mar 2010 4:42 PM

JanetK49,

I just kind of popped into your thread on the cracked paint, and hadn't read previous postings, so didn't know you were using water-mixable oils. I'm assuming, from your statement, that water-mixables is what you used on this painting. Even so, it may not matter. If the cause of the cracks can be correctly diagnosed, then it may be possible to repair it so no future repairs are needed. Art conservators fix lots of worse conditions than this, though such repair comes at a cost.

Question? How heavy an impasto is this? Is the paint really thick? If it was painted, what did you say, over 20 years ago? It should be totally cured. HOWEVER, if the cracks are perceptibly, measurably getting worse, I suspect that it's beginning to release from your canvas a bit. It the paint is really thick, it might continue to shrink for a long time, and if you used water-mixable oils, the paint layers initially will shrink a bit anyway (just like acrylics do) as whatever water is mixed into the paint evaporates out of it.

As to the Alkyd medium:  Liquin is made by Winsor & Newton. It was formulated as a painting medium for their line of alkyd artists colors, probably the first to go on the market, around 1978. Alkyd is a synthetic resin that forms an emulsion with mineral spirit or turpentine, can be mixed and blended like oils, mixed and blended WITH traditional oil paints, but lends the quality of much faster drying than traditional oils. It combines some of the best characteristics of both oil and acrylic, but in truth, is neither. Whereas acrylic applications will dry in an hour or two, alkyds will dry in about 24 to 36 hours. The fact that it is compatible with oil paint is why it is ideal for this repair application.

A close examination of the cracks, with magnification, may tell you what you need to know. If you can see the surface of the canvas in the middle of the crack, then the paint layer is in danger of separating from the canvas itself. The alkyd medium can be used a bit like glue in this case, similar to how some artists use the various acrylic mediums, which make a great glue for things like decoupage. In the case of your painting, the Liquin should be thinned with a touch of mineral spirit so it flows easily down into the cracks; you want it to get all the way to the bottom, in order to strengthen what adhesion remains. Liquin just from the bottle looks irregularly gloppy (almost lumpy, with both thin and thick consistencies. Pour about a tablespoon or two into a large open palette cup, and add mineral spirit with an eyedropper, two or three drops at a time, and stir the Liquin after each addition, until it is a slightly runny, but even, consistency, that will drizzle off the end of the palette knife back into the cup. This should be liquid enough to get down into the cracks and cement whatever loosening may have taken place. Just be sure that it gets down into it. It should fill up the cracks and the excess can be wiped off, or spread out a bit with a brush. Be sure and suspend your brush in thinner soon so the alkyd doesn't dry in it.

I just remembered that in an earlier post, I thought you mentioned something about sizing the canvas with rabbit-skin glue, is that correct? If so, part of the problem may be related to using water-mixable oils over this. I realize that after the glue sizing, one should add two or three coatings of TRADITIONAL gesso, not acrylic "gesso". Rabbit-skin glue's major shortcoming is that it is hygroscopic, meaning it shrinks or swells with changes in humidity and temperature. Unless the gesso completely covers this sizing, some water from the paint mixtures may have affected some of the sizing. In addition, the painting being hung on an outside wall may have contributed to the cracking and separation of the paint layer (if any, not yet determined). The atmosphere BEHIND a painting hung on an outside wall (particularly with the temperature extremes of the north) means that it's several degrees colder on its back side, than on its front side, and the humidity on both sides will be different as well. Think about that for a minute. That creates a strangely difficult environment for a painting to maintain stability, further complicated by the rabbit-skin glue sizing. The whole canvas surface is constantly in flux. I would suggest that if you want to continue using water-mixable oils, that you use acrylic gesso as priming for your canvases. It does not suffer from the shrink-swell problems of rabbit skin glue.

It might be worth making a few calls to find an art conservator to consult about this. A university, state art commission, or museum may be able to link you up with an art conservator.

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JanetK49 wrote
on 14 Mar 2010 11:05 AM

wwmccoy,

The original painting was done with traditional oils, not water mixable oil.  And any repairs I do to the cracking will also be done with traditional oils.  (Luckily, I remember which colors I used for that top layer of paint so shouldn't have to buy lots of traditional paints.)  I will be looking at the cracks under a magnifying glass per your previous suggestion, but the last time I had the painting off the wall, the ground seemed fine.  And the only thing I could see in the cracks was the white under painting. 

Now, that under painting as I said previously was probably Permalba or Titanium white with a bit of earth tone (burnt sienna/yellow ochre/burnt umber) mixed in.  I didn't use any medium when I was painting usually so the thickness of the paint would simply be enough to cover the surface of the canvas and not built up thickly.  I also remember that the dark paint over was a single layer and also not built up.  It did have medium mixed in so it was a bit thinner than the under painting which I thought would be enough to fulfill the "fat over lean" rule.

I hope that anyone reading this thread takes my experience as an object lesson - yes, your paintings can crack in your own lifetime and not centuries from now.  A great example of what not to do!  :)

Again wmmccoy, thank you so much for the good advice on how to do this repair and what to look for. 

JanetK49

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wmmccoy wrote
on 14 Mar 2010 2:13 PM

JanetK49:

Now that I understand more clearly what was involved in your painting, a couple of things occur to me: (1) the components of Permalba (which I use and love myself) is made from BOTH titanium oxide AND zinc oxide. I don't remember the proportions, but the addition of zinc adds an element of brittleness to the behavior of Permalba, when unmixed with significant amounts of any other colors. The zinc is added to the mix to lend a bit of brilliance to the paint, since it has a slightly bluish cast, thus appearing more "white". The brittleness effect can be demonstrated if a thin layer of Permalba is spread on a piece of glass and allowed to completely dry. Start scraping it off with a razor blade, and the edges of the patch of color will "shatter" as it is scraped off the glass. Other colors may scrape off in a single layer without shattering, and possess a leathery feel. The fact that the colors you mixed into it (burnt sienna, yellow ochre and burnt umber) are all low-oil absorptive earth colors probably didn't help. The overpainting must have been done when the underpainting was dry, or nearly dry, for there to be such a distinction in color, i.e., that the cracks show up as white, through the darker overpainting. That use of a near pure underpainting of Permalba or even titanium alone, set up the problem created by (2) the fact that it was hung on an outside wall, where the rabbit-skin glue sizing, being sensitive to humidity and variations in temperature, cause enough "shrink-swell" cycles to eventually cause the paint layer actually ON the surface of the canvas (the predominately white layer) to crack; no different than freeze-thaw cycles will cause rocks to crack.

Titanium white alone is less brittle than blends of titanium and zinc. And, zinc white alone creates a pretty fragile surface if used as pure color. The most durable white is lead white, sold as Flake White or (inaccurately) Cremnitz White. These both (as currently formulated) contain lead, and while toxic, can be used safely as long as proper care is taken in handling it. Lead white is a little creamier in color than titanium or zinc, and has a stiffer consistency, but is highly opaque; a characteristic that neither Titanium White nor Zinc White have. Ground in linseed oil, lead white is incredibly durable (lead white house paint easily lasts for more than a century, while exposed to the weather). It was the primary artist's white in use until around 1921, when titanium oxide was prepared for artists' use. Zinc white had a use in watercolor before this, but getting it to work in oil colors took a while to perfect. 

So technically, your problem boils down to (1) paint with some characteristics of brittleness, and (2) an unstable support hung against an outside wall, constantly shifting due to changes in humidity or temperature or both. This combination of factors led to and promoted the cracking. The lack of varnishing may have also contributed to it as well. Had the painting been varnished as soon as it was fully dry, the layer of varnish might have helped "cement" and add some stability to the paint layer, though the sizing shifting and the brittleness might still have caused cracks to appear. You also worked on it in stages "added heft to his arm" so there were distinct layers that were not blended into each other. These behave like rock strata, where though stacked, may have different components and densities and some more brittle and crumbly than others, thus unstable, because they have no common ties holding them together. This is why "alla prima" painting wet-into-wet is the ideal. All the paint is on the support as a single, contiguously-drying layer, and is therefore, more stable.

My observations for your consideration, along with your continuing research. 

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JanetK49 wrote
on 9 Aug 2014 11:29 PM

To all I heard from 4 years ago:

The good news is that I did fill in the cracks that were on the painting.  The orginal was done in traditional oil paints, while I used water mixables on the fill ins.  I over painted the cracks (it was too tedious to try to do just the white cracks) and there didn't appear to any problem using the different type of paint.  I waited an appropriate time and then sprayed the entire painting with Soluvar.  The cracks disappeared like magic and the painting once again looked fresh.  It stayed that way for many months.

The bad news is that the painting was destroyed a couple of months ago along with all my other paintings, equipment, supplies, etc., when the building in which I had my studio was gutted in a fire.  Yes, I was insured (I strongly suggest everyone have insurance) and I have set up shop elsewhere replacing supplies and equipment as needed.  I'm posting this to let you all know that your discussion and suggestion helped me fix the painting and I believe that the fix would have held indefinitely.

Oh, the other good news is that the painting of my late husband reading a magazine on a chaise lounge, which some of you referenced,  was on loan for a group show at the Detroit Historical Museum and so survived.

Thanks again for all your help and Happy Painting!

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