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  #16   Report Bad Post  
Old 12-04-2017, 08:35 AM
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Gigalot Gigalot is offline
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Re: Cleaning an Unvarnished Oil Painting?

Or, you can follow Bill's advice and try to varnish your painting to help future cleaners to remove old varnish with all it's dust, scratches, fly-ass and finger prints. With the sacrifice of some percentage of surface paint...
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Old 12-04-2017, 08:48 AM
sketch1946 sketch1946 is offline
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Re: Cleaning an Unvarnished Oil Painting?

Quote:
Attempts to maximize desirable properties in paints have led to considerable alteration from the basic formula of a simple oil and pigment mixture.

Each alteration may have both an immediate consequence in the early behavior of the paint and a long-term one that may produce undesirable results.

Originally, the ability of paints to form dry films depended upon ...a larger amount of linolenic acid ...and to some extent, linoleic acid.
The unsaturated bonds, via an oxidation process, cross-link to form a tangled three-dimensional network.

On the other hand, the ester bonds are important to the overall structural integrity of the dried oil film.
However, these bonds may be easily hydrolyzed during and after the polymerization reaction, releasing free fatty acids.
If hydrolysis of the ester bonds occurs before the film forms, the system becomes
more acidic and may react with some of the pigments present in it.

Are the other oils, sunflower, safflower, poppy and walnut oils a safe substitute for linseed oil?

Quote:
This weight loss from oil paint films predicts that over time the linseed oil–based paints will be less affected by diffusion of solvents than the poppy oil– or walnut oil–based paints because of a smaller loss of weight.

Figure 1 plots the long-term weight loss in several oils over 1200 days.

Note that the cold-pressed linseed oil loses far less weight than the other ones.
Some of the oils are lighter in weight than when first applied, indicating severe degradation of the oil film polymer, which can continue for several years.

What solvents will attack dried oil paint?

Quote:
Table 1 shows the reactions of selected paints made with
100% hydrolyzed linseed oil and different pigments, such as
red iron oxide, burn umber, smalt, and raw umber. These paints
mimic the worst case since all the ester bonds are hydrolyzed.

The paints were immersed in the solvent for 5 minutes.

Acetone is the most aggressive solvent, to the point that the
paints decompose after treatment. The toluene-treated paints
were very embrittled and decomposed with the application of
mechanical force.

Water and hexane, both rather mild solvents,
did not affect the paint films.

https://repository.si.edu/bitstream/...enburg.Web.pdf
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Old 12-04-2017, 09:27 AM
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Gigalot Gigalot is offline
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Re: Cleaning an Unvarnished Oil Painting?

Quote:
Originally Posted by sketch1946
What solvents will attack dried oil paint?

https://repository.si.edu/bitstream/...enburg.Web.pdf
Water will attack crack lines, natural resins and moisture sensitive barriers between oil paint and acrylic/glue primer. That can cause varnish matting and paint flaking.
BTW, Calcium carbonate putty mixture did not live up to our expectations to form improved films. As well as pure Litharge addition. While high Manganese content and Copper content can do the job.

Last edited by Gigalot : 12-04-2017 at 09:40 AM.
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Old 12-04-2017, 09:40 AM
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Humbaba Humbaba is online now
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Re: Cleaning an Unvarnished Oil Painting?

Before attempting to clean an oil painting, it is wise to take several good quality pictures of the work. In case you damage part of it, or all of it, you can proceed to use these images to restore the painting, this way you cover your sins.

If you want a tough solid oil painting film, use Linseed, and Stand Oil. Resins such as Dammar, Canada Balsam make the paint film susceptible to solvents.

I use Walnut Oil for glazing, but only after cooking it with Amber.
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Old 12-04-2017, 01:52 PM
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Re: Cleaning an Unvarnished Oil Painting?

http://www.tate.org.uk/about-us/proj...le-modern-oils
Lovely!
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Old 12-06-2017, 03:50 AM
sketch1946 sketch1946 is offline
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Re: Cleaning an Unvarnished Oil Painting?

Haha, I found a great section on cleaning oil paintings, about eight pages of it, in the back of Ralph Mayer's Handbook of Materials and Techniques, third edition 1975 page 508:

I didn't find any instructions on how to clean an unvarnished painting,
basically Ralph just assumes that oil paintings are varnished....

his recommendation is don't leave it longer than one year to varnish a painting, and he feels it's better to varnish too soon than too late...

however, he doesn't recommend using water to clean a varnished painting, he describes a variety of solvents and working methods to clean varnished paintings, he says it's undesirable to remove all the previous varnish layer, and describes leaving an extremely thin layer of varnish intact when 'cleaning' a painting, before covering with one or more layers of fresh varnish...

Last edited by sketch1946 : 12-06-2017 at 03:55 AM.
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Old 12-07-2017, 06:41 PM
Luis Sanchez Luis Sanchez is offline
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Re: Cleaning an Unvarnished Oil Painting?

As the other posts mention, avoid water even if it looks like a simple "solution". For properly dried paintings (and yours are 5-7 years old, so they should be dried unless super duper impasto was used)a lint free cloth + gamsol should help. Try the mildest solvent around, which will be a form of OMS. Another tried and true method is just using a piece of bread as a sponge. Take in mind that both methods only remove surface dust and wheter one uses a cloth with gamsol or bread, absolutely no force should be used. You want to remove dust, not push it inside the painting.

Beyond that, it would be better to send them to the pros.
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Old 12-07-2017, 07:59 PM
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Humbaba Humbaba is online now
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Re: Cleaning an Unvarnished Oil Painting?

Quote:
Originally Posted by Richard P
I know some conservators use special gels to pull off dirt and debris from the painting surface. I almost wonder if plain old PVC glue would work to get some of it off?

I haven't found a reference to what you describe. However, I can confirm the use of a Kneaded eraser to remove dirt.

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Old 12-08-2017, 03:35 AM
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Re: Cleaning an Unvarnished Oil Painting?

Quote:
Originally Posted by Humbaba
I haven't found a reference to what you describe. However, I can confirm the use of a Kneaded eraser to remove dirt.

That makes strong mechanical stress to paint surface with a combination of abrade affect. I will never try such things to clean any oil paintings.
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Old 12-08-2017, 11:40 AM
Richard P Richard P is offline
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Re: Cleaning an Unvarnished Oil Painting?

Quote:
Originally Posted by Humbaba
I haven't found a reference to what you describe. However, I can confirm the use of a Kneaded eraser to remove dirt.


Have a look at this:
http://www.conservation-wiki.com/wiki/Gels
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Old 12-12-2017, 01:31 PM
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Phil Brink Phil Brink is offline
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Re: Cleaning an Unvarnished Oil Painting?

Quote:
Originally Posted by Richard P

looks very promising. I look forward to nerding out on those articles. SCIENCE!
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