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Old 05-29-2008, 11:25 PM   #31
Michele Rushworth Michele Rushworth is offline
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Thanks, Virgil.

I have been oiling out with linseed, but in this cool, wet Seattle climate it can take literally weeks for the oil to dry enough for the painting to ship, even if the paint underneath is already dry. Then if it sinks in again, and I have to re-oil, that's another two weeks for drying. Meanwhile, deadlines are looming!

I tested the Galkyd Lite/OMS mixture for oiling out earlier this week and thankfully it's dry to the touch in two days.
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Old 05-31-2008, 12:30 AM   #32
Virgil Elliott Virgil Elliott is offline
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Quote:
Originally Posted by Michele Rushworth
Thanks, Virgil.

I have been oiling out with linseed, but in this cool, wet Seattle climate it can take literally weeks for the oil to dry enough for the painting to ship, even if the paint underneath is already dry. Then if it sinks in again, and I have to re-oil, that's another two weeks for drying. Meanwhile, deadlines are looming!

I tested the Galkyd Lite/OMS mixture for oiling out earlier this week and thankfully it's dry to the touch in two days.
Michele,

It sounds like you're oiling out in order to even the gloss instead of to re-saturate the colors and lubricate the surface for continuing to paint on it. If that's what you're doing it for, I suggest spraying a thin coat of retouch varnish instead. Gamblin's Gamvar would work well for that purpose, perhaps thinned a bit more with mineral spirits and shot through a spray gun or large airbrush. It will even out the surface gloss and certainly dry faster than oil. Spraying it on eliminates the risk of the brush and solvent damaging the paint..

Alkyd mediums are not intended to be used as varnishes.

Virgil
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Old 06-03-2008, 01:06 PM   #33
Michele Rushworth Michele Rushworth is offline
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Virgil, what's the downside of using alkyds as a varnish? If they're non-yellowing they would never need to be removed, right? Gamblin recommends using that 50/50 Galkyd Lite/OMS mixture as a retouch varnish. What if, after doing that, the painting then had sufficient overall gloss that it didn't need a final varnish?
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Old 06-03-2008, 03:01 PM   #34
Richard Bingham Richard Bingham is offline
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Not to leap-frog a reply from Virgil, Michele, but a "final varnish" has a function above whatever integrity the paint films that comprise the painting may have, and that is to be a removable barrier between the painting and subsequent wear and tear.

As for the question of whether alkyds yellow, you can quite easily test the materials you are using. Apply a film of alkyd medium to a small piece of glass . . . make a few. Place one outside in full weather, another where it gets a lot of sun in an interior setting, and a third someplace where it's dark and damp. Within a few weeks, differences will begin to show if the material is "fragile". If it's tough stuff, it may take a few months to see changes.
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Old 06-03-2008, 03:04 PM   #35
Michele Rushworth Michele Rushworth is offline
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Thanks, Richard!
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Old 06-03-2008, 04:34 PM   #36
Virgil Elliott Virgil Elliott is offline
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Quote:
Originally Posted by Michele Rushworth
Virgil, what's the downside of using alkyds as a varnish? If they're non-yellowing they would never need to be removed, right? Gamblin recommends using that 50/50 Galkyd Lite/OMS mixture as a retouch varnish. What if, after doing that, the painting then had sufficient overall gloss that it didn't need a final varnish?
Michele,

The potential downside is that if the alkyd resin does ever develop a defect of any kind that interferes with the viewing of the painting itself, it will have to be removed, and alkyds require very strong solvents to remove. Thus there would be increased risk to the paint layer. Yellowing is not the only concern, but we cannot say with certainty that it won't yellow over the long term, or crack, or cross-link and become less transparent. It's also a fast-drying substance, and carries the possibility of interfering with the thorough drying of the paint underneath. Of at least equal importance to "fat over lean" is slower-drying over faster-drying. Doing it the other way around can lead to various problems.

I'm sure Gamblin's advice regarding the use of their alkyd medium as a retouch varnish was intended to mean as a couch to paint into while the painting is in progress, as in oiling out over a dried layer in order to re-saturate it to facilitate precise color-matching and to lubricate the surface so new paint will blend into the image more seamlessly. I would still question the advisability of using alkyds for that purpose on any painting whose paint layers have not cured sufficiently. Linseed or walnut oil would be safer choices, in my opinion, with the proviso that as much should be wiped or blotted off as will come off with a dry rag or paper towel immediately after it's brushed on. Very little is needed to accomplish its purpose. Whereas you might get by with using alkyd medium for that purpose, why take the chance? You went to a great deal of trouble to paint the picture, and your collector is probably paying a good price for it. Why risk screwing it up?

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Old 06-03-2008, 04:41 PM   #37
Virgil Elliott Virgil Elliott is offline
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Quote:
Originally Posted by Richard Bingham
Not to leap-frog a reply from Virgil, Michele, but a "final varnish" has a function above whatever integrity the paint films that comprise the painting may have, and that is to be a removable barrier between the painting and subsequent wear and tear.

As for the question of whether alkyds yellow, you can quite easily test the materials you are using. Apply a film of alkyd medium to a small piece of glass . . . make a few. Place one outside in full weather, another where it gets a lot of sun in an interior setting, and a third someplace where it's dark and damp. Within a few weeks, differences will begin to show if the material is "fragile". If it's tough stuff, it may take a few months to see changes.
Richard,

That's good advice. I'd suggest extending the test over a period of at least a year, preferably longer. Some of my tests have involved as much as 23 years. That gives me a pretty good idea which materials will outlast which over the long term.

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Old 06-03-2008, 04:59 PM   #38
Michele Rushworth Michele Rushworth is offline
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Thanks, Virgil!
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Old 06-03-2008, 04:59 PM   #39
Richard Bingham Richard Bingham is offline
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Exactly, Virgil. You're definitely right about the length of time involved. Good stuff can take a long, long time for failure modes to appear, and it's really instructive in the meantime.

Testing is something of a necessity, if one truly wishes to know the nature of materials As with so many other things, a wide range of quality often exists, but our tendency is to accept simply identifying materials as species and leaving it at that. That's as naive as identifying a liquid as "wine", ignoring the gulf that separates stuff some homeless guy under a bridge is guzzling from the fine vintages offered in a four-star restaurant.
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Old 09-23-2008, 10:05 PM   #40
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