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Old 06-19-2010, 05:05 PM
Nilesh Nilesh is offline
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Polyurethane Varnishes?

Derivan has water-based polyurethane varnishes, MM19 and MM11. MM19 is described as a:

Water-based polyurethane varnish with a non-yellowing hard wearing high gloss finish (for use on rigid surfaces only)

There is additional information here: http://www.derivan.com.au/pages/varnishing.html

Other companies also offer water-based polyurethane varnishes, and there are solvent-based polyurethanes that could also be used as protective coatings or varnishes.

The water-based versions might be useful for those who want or need to avoid solvents.

If anyone has tried these, or decides to try them, please feel free to post.

Some of the others are listed here:

http://www.hofcraft.com/paintingacce...-varnishes.htm

Last edited by Nilesh : 06-19-2010 at 05:08 PM.
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Old 06-19-2010, 08:46 PM
Nilesh Nilesh is offline
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Re: Polyurethane Varnishes?

After doing some more research on these varnishes, it appears that the solvent-based polyurethanes (some of them at least) may have archival issues -- problems with yellowing, for example, and also serious or concerning levels of cross-linking over time.

The water-based polyurethanes, however, are said to be non-yellowing. It is unclear though (at this point, at least) whether cross-linking is a problem with them or not -- there may or may not be information available that would clear up this issue. It may be out there, but I haven't seen it yet.

It is also unclear, at this point, how they compare with solvent-based acrylic varnishes in archivalness.

If anyone finds more information on these or related points, please feel free to post.

Last edited by Nilesh : 06-19-2010 at 09:03 PM.
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Old 06-20-2010, 12:06 AM
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Re: Polyurethane Varnishes?

I have some of that, but since it is not for use on canvas I've never used it. Bought a large pail of it too.
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Old 06-20-2010, 12:50 PM
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Re: Polyurethane Varnishes?

i used it when i lived in arizona and many miles away from an art supply store. The polyurethane perfomed well enough but at the time (1997) i worried about its archivalness and went back to medium.
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Old 06-21-2010, 02:31 PM
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Polyurethane varnishes are basically the choice for craft-type projects on a rigid material, being relatively inexpensive, easy to get (available pretty much everywhere) and tough as old boots.

But they're not suitable for fine-art applications using the normal criteria.

Quote:
Originally Posted by Nilesh
After doing some more research on these varnishes, it appears that the solvent-based polyurethanes (some of them at least) may have archival issues -- problems with yellowing, for example...
That might be where there's full-time exposure to daylight. And types are available with UV-resistant additives.

Quote:
Originally Posted by Nilesh
...and also serious or concerning levels of cross-linking over time.
To what type of paint(s)?

This and any other negatives are really beside the point though if the intent is to use them for paintings, since polyurethane doesn't have one of the prime attributes for fine-art varnish: removability.

The varnishes offered by various companies based on synthetic resins that are soluble in mineral spirits - both LMW and HMW types - are basically the only choice in terms of resistance to yellowing and ease of removal down the line.

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Old 06-21-2010, 05:23 PM
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Re: Polyurethane Varnishes?

use it for years on harboard masonite paintings with no problems...
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Old 06-29-2010, 03:48 PM
Nilesh Nilesh is offline
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Quote:
Originally Posted by Rob Lineberger
I have some of that, but since it is not for use on canvas I've never used it. Bought a large pail of it too.

If you ever choose to mount canvases on rigid supports or backing (which is an approach that is highly recommended by Gottsegen), you might be able to use it on those canvases.


Quote:
Originally Posted by ribeyedsmile
i used it when i lived in arizona and many miles away from an art supply store. The polyurethane perfomed well enough but at the time (1997) i worried about its archivalness and went back to medium.

It seems as though Derivan is offering water-based polyurethanes that they might consider suitable for fine art applications, but it is not entirely clear exactly how they regard it in terms of archivalness. It would be interesting to hear what they have to say about it. If anyone emails them, or finds details on this, it would be interesting to hear more -- please feel free to post.

The world of polyurethane chemistry, chemical engineering, research, development, innovation is vast. There are new products coming out all the time, and some of them are probably much better suited to fine art applications than others. Derivan seems like a good company, with some excellent acrylic and other products, including those for fine art applications.


Quote:
Originally Posted by Einion
...But they're not suitable for fine-art applications using the normal criteria....
I'm not so sure this is true. It would certainly depend on the individual product to a large extent, and also on the application and specific situation and artist.

Golden recognizes this and recommends polyurethanes for some applications, including fine art applications.

Quote:
Originally Posted by Einion
That might be where there's full-time exposure to daylight.

Not only where there is full-time exposure to daylight, though. And there could be other factors involved as well.

Quote:
Originally Posted by Einion
This and any other negatives are really beside the point though if the intent is to use them for paintings, since polyurethane doesn't have one of the prime attributes for fine-art varnish: removability.

But it doesn't follow that they are beside the point: there may be other characteristics and advantages that outweigh the (widely supposed) non-removability.

There are also some very interesting and rarely discussed points, and some more-nuanced thinking in relation to the removability issue. Will post more on that later.

Quote:
Originally Posted by Einion
The varnishes offered by various companies based on synthetic resins that are soluble in mineral spirits - both LMW and HMW types - are basically the only choice in terms of resistance to yellowing and ease of removal down the line.

I would have to disagree with this. Some of the polyurethanes resist yellowing rather well, according to tests done by Golden and others. And there is much more to the removability issue than meets the eye, and more than I have seen anyone discuss here in these forums thus far.

Not only that, but there are also ways of rendering the protective (and superior in their protection) polyurethane systems easily removable.


Quote:
Originally Posted by IRDOC
use it for years on hardboard masonite paintings with no problems...

DOC,

Glad to hear it!

They have a lot of potential as protective coatings, including for fine art applications.

Last edited by Einion : 06-30-2010 at 04:57 AM. Reason: Merged posts
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Old 06-29-2010, 05:07 PM
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Re: Polyurethane Varnishes?

could be fine for a final non-removable varnish.

possible issues which need clarification by whatever manufacturer one might choose is:

yellowing
cracking
adding a removeable varnish on top
brittleness if on canvas
long term adherence to acrylic paints

But again, these questions would be answered by the particular brand chosen
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Old 06-30-2010, 05:18 AM
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Quote:
Originally Posted by IRDOC
use it for years on harboard masonite paintings with no problems...
So, the obvious question: ever had to remove it?


Quote:
Originally Posted by Nilesh
Quote:
Originally Posted by Einion
...But they're not suitable for fine-art applications using the normal criteria....
I'm not so sure this is true. It would certainly depend on the individual product to a large extent, and also on the application and specific situation and artist.
I was very careful to include the last bit; one of the prerequisites for fine-art varnishes is removability. And to be clear here: this is easily removable (with the use of weak, non-polar, solvents for those unfamiliar with this area) which common polyurethanes are not.

Quote:
Originally Posted by Nilesh
Golden recognizes this and recommends polyurethanes for some applications, including fine art applications.
For outdoor work for example PU seems about the only suitable choice to me too, assuming varnishing is desired. But that's not to say that the same product is then a reasonable option where that level of protection is not needed, which is what I was getting at.

I don't think we should loose sight of the fact that the varnishes soluble in mineral spirits that are sold to artists provide good enough protection for paintings under average or typical hanging conditions. More resistance to abrasion for example, while it might be desired by some users, isn't normally required and MSA or Soluvar or Gamvar (as well as all similar varnishes of the same types) are certainly fit for purpose, without any notable downsides.

Quote:
Originally Posted by Nilesh
Quote:
Originally Posted by Einion
This and any other negatives are really beside the point though if the intent is to use them for paintings, since polyurethane doesn't have one of the prime attributes for fine-art varnish: removability.
But it doesn't follow that they are beside the point: there may be other characteristics and advantages that outweigh the (widely supposed) non-removability.
Okay, granted: obviously individuals will weigh the pros and cons of anything differently (even for the same applications) but AFAIC if you discount something on one ground the other reasons for also ruling it out are then beside the point

The non-removability of PU is not just supposed though. As far as the typical product goes, especially types intended for use on floors, they are the very epitome of hard to remove.

Since my original comment was a follow-up point to this I'll ask again, the "serious or concerning levels of cross-linking over time" that you mentioned, are to what type or types of paint?

Quote:
Originally Posted by Nilesh
And there is much more to the removability issue than meets the eye, and more than I have seen anyone discuss here in these forums thus far.
I think along those lines it's worth reviewing the conservation literature, even if simply for an overview of what they still use and why and what they don't. Although occasionally there are specifics given about why a product isn't used any longer or is less favoured often we have to infer why they don't make use of something, but the general attributes they look for are quite clear.

Quote:
Originally Posted by Nilesh
Not only that, but there are also ways of rendering the protective (and superior in their protection) polyurethane systems easily removable.
Such as? Modified by the user in an off-the-shelf product? Easily removable by what means?

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Old 07-01-2010, 05:32 PM
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Re: Polyurethane Varnishes?

Hate to be a fly in the ointment, but...

Seriously, how many paintings produced by artists posting here (including myself) would actually need the varnish removed at a later date and for what possible reason? I have decades old acrylic works that are varnished and there is zero yellowing happening to them (after re-framing some of them, the frame usually protects edges from yellowing).

Isn't this usually done for conservation reasons on very old works that are supposed to be actually well-worth the expense, time and trouble it would take to do such a thing? Are any of us really doing works that actually rate this process or have been around long enough to need conservation? Aren't acrylic and oil paints (and varnishes) vastly superior and much more stable now, chemically-speaking, than 50 years ago?

Am I missing something here? :-/ (buzzing off now...)
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Old 07-01-2010, 06:54 PM
Nilesh Nilesh is offline
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Re: Polyurethane Varnishes?

After a period of (almost too much) research recently, my perspectives on varnishing in general and polyurethanes in particular have changed significantly, even dramatically.

Thanks goes out to Rhéni Tauchid and her book for challenging many of the stale dogmas about varnishing. She may be wrong on some points, but still -- paradigm shifts are great, especially when you really get your feet wet.

One game-changer is the fact that polyurethanes are, in fact, removable. They have been and continue to be removed by art conservators and others. In the future, as information technologies and information availability matures (and the brilliant staff at the Good Ship Google continues with it projects), it will become easier and easier.

Conservators have made it very clear to me that their field is advancing rapidly as various technologies, experiments, experimental results, experimental knowledge, enzyme chemistry, nanotechnology, new equipment and techniques, etc. all continue to evolve and progress. New developments and important advances occur within much shorter time frames than eighty or one hundred years.... There is a lot more that could be said on this, but there is enough on the plate already, and time is limited.

***
My varnishing system of choice, for most projects and applications, would now be a carefully selected polyurethane, possibly coated with conservator-approved microcrystalline, synthetic, semi-sythetic, or hybrid waxes.

Why?

Just as Golden has made it clear that their Hard MSA Varnish is significantly harder and more durable, and forms a tighter film than the standard (usually used) and more porous MSA varnishes, and just as they make it clear that the standard MSA varnishes are likewise superior to the polymer varnish, so it is clear that these polyurethanes are superior in these same areas, not only to the polymer varnish and the standard MSA varnishes, but also to the Hard MSA Varnish itself. This can be useful for indoor paintings (including the typical indoor paintings) as well as outdoor ones. This last point has been thought this through rather carefully, and it has become clearer and clearer that there are many common instances in which these advantages would be real rather than merely theoretical.

The waxes are one of the more interesting, surprising, and useful discoveries I have made in a long time. Thanks goes out to the staff at Golden for pointing them out and testing them.
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Old 07-01-2010, 07:04 PM
Nilesh Nilesh is offline
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Re: Polyurethane Varnishes?

Quote:
Originally Posted by it'sALLart
Hate to be a fly in the ointment, but...

Seriously, how many paintings produced by artists posting here (including myself) would actually need the varnish removed at a later date and for what possible reason? I have decades old acrylic works that are varnished and there is zero yellowing happening to them (after re-framing some of them, the frame usually protects edges from yellowing).

Isn't this usually done for conservation reasons on very old works that are supposed to be actually well-worth the expense, time and trouble it would take to do such a thing? Are any of us really doing works that actually rate this process or have been around long enough to need conservation? Aren't acrylic and oil paints (and varnishes) vastly superior and much more stable now, chemically-speaking, than 50 years ago?

Am I missing something here?....
These seem like valid points; but there are also some valid reasons for wanting to present a client with a painting that maintains its appearance and integrity as long as possible, and is as easy to clean and maintain as possible, within reason (which will vary from artist to artist) or practicality.

Quote:
Originally Posted by Einion
I was very careful to include the last bit....

Yes, I had noticed that; but earlier you also said ...since polyurethane doesn't have one of the prime attributes for fine-art varnish: removability.

[Aside: First, let me express my appreciation for the civilized tone and discussion here. Too many people seem unable to remain civilized through discussion that challenges held-notions, and through making inquiries into new territory, and I often tend simply to exit when this happens. So thanks for keeping it on a civilized keel.]

One question would be: Are (some) polyurethanes (the ones that are actually being used in a specific instance) removable? Or are they all 'non-removable' in a strict sense?

Another question would be: Are they easily removable.

Then there is the matter of defining or clarifying the word easily.

And there is also the question of how 'easy' it is to remove the (supposedly easily) 'removable' solvent-based acrylic varnishes. For some (many) artists, including some on these forums who have talked about this, it is not easy at all. There are various reasons why solvents may be disallowed or undesirable in their working spaces or classrooms. Many acrylic artists are not fans of using solvents in the first place, and use acrylics (they often talk about this) in part to get away from solvents.

Is it 'easy' for them?

How easy is it for them to apply the varnish? And how easy is the removal procedure (there is an artist here who has talked about this)? And then there is the business of re-application (which is often omitted). There are artists here who simply find the whole process undesirable in one way or another.

And what if there were a varnish significantly less likely to need removal in the first place, and one that did not involve solvent exposure for application?

Which would I rather have: A varnish that is likely to need to be replaced more often but is 'easier' to remove, or a varnish that is less likely to need replacement but is 'harder' to remove (but in some cases might actually be quite easy to remove), but easier (or more practical, lower in health risks, or in other ways more desirable) to apply, and also provides better protection [in various ways, not only from abrasion, scuffing, scraping, moving, transport, packing, blocking, stacking, accidents, particle embedding, and stains, but from more (including molds) as well] for the underlying layers of acrylic paint, or painting itself?

There are a lot of unexamined aspects and possibilities here.

There is also the matter of varnish porosity, which itself has various aspects.

There is more, but I'm out of time....

Last edited by Nilesh : 07-01-2010 at 08:04 PM.
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Old 07-01-2010, 11:05 PM
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Re: Polyurethane Varnishes?

Quote:
Originally Posted by Nilesh
there are also some valid reasons for wanting to present a client with a painting that maintains its appearance and integrity as long as possible, and is as easy to clean and maintain as possible, within reason...

Since we all won't be around when that kind of thing really starts getting important (say, about 70 to 100 years from now) it's certainly debatable.

Question: Has anyone here had to remove the varnish on a painting of theirs in the last 20 years and if so, why?
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Old 07-02-2010, 03:46 AM
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Einion Einion is offline
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Quote:
Originally Posted by it'sALLart
Hate to be a fly in the ointment, but...

Seriously, how many paintings produced by artists posting here (including myself) would actually need the varnish removed at a later date and for what possible reason?
...
Are any of us really doing works that actually rate this process or have been around long enough to need conservation?
I know what you're getting at but at least one poster here has mentioned having to remove a varnish on a recent work because of damage to the surface during shipping to or from a show. Physical damage of some kind is the simplest reason (and the one most likely to show up in the short term) for the need for removability, separate from conservation/restoration considerations later on in a painting's life.

Assuming work is not important enough to rate conservation is perhaps a valid consideration in all fairness for leisure painters, but there's simple good working practice to factor in - use the best materials you can.

Some people aren't bothered by archival considerations and that's fine, but most of us at least make some nod to it by not painting on cardboard or another very dodgy substrate, using quality artists' primer and using artists' acrylics instead of wall paint. So any reason not to include varnishing under the same umbrella?

Quote:
Originally Posted by it'sALLart
Isn't this usually done for conservation reasons on very old works that are supposed to be actually well-worth the expense, time and trouble it would take to do such a thing?
Varnish removal and replacement is generally required around the 50-year mark. With all older varnishes (and some newer ones!) it becomes more and more necessary to remove the old varnish because it has begun to degrade in some way: 1, discolouration - not just yellowing, but actually going brownish in some cases; 2, cracking or other physical failures; 3, dust intrusion and other contamination; 4, changing chemically and becoming harder to remove, forcing the need to use stronger solvents that pose more of a risk to the paint layer.

Obviously 1 is the best-known issue with varnishes historically and probably the most evident problem at a glance (although some discolouration might actually not be that obvious on some paintings if it's fairly uniform - "gallery glow"). But with newer varnishes of one kind or another this shouldn't show up typically so it'll probably come down primarily to 3 these days, which to make a generalisation will occur.

Quote:
Originally Posted by it'sALLart
Aren't acrylic and oil paints (and varnishes) vastly superior and much more stable now, chemically-speaking, than 50 years ago?
Not necessarily, sort of and yes, respectively

Just to focus on varnishing, the spirit-soluble ones now available to us for example are a major advance for acrylic painters because prior to their introduction there was a real problem in deciding what (if anything) to use to protect the painting's surface.


Quote:
Originally Posted by Nilesh
One game-changer is the fact that polyurethanes are, in fact, removable.
They are of course removable, they're removed from floors and furniture every day Like I clarified, the question is are they easily removable? And the common methods to remove polyurethane - and importantly, all of those available to the man on the street - would pose an unacceptable risk to acrylic paint.

Now about that modification to make them easier to remove you mentioned...?

Quote:
Originally Posted by Nilesh
...polyurethanes... have been and continue to be removed by art conservators...
I can assure you that they'd prefer not to have to

There are other open questions that I presume you'll be returning to answer so I'll leave it at that for the time being.

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Old 07-02-2010, 08:43 PM
Nilesh Nilesh is offline
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Re: Polyurethane Varnishes?

Another possibility I didn't have time to get to yesterday is using Gamvar over polyurethane, which gives the best of both worlds -- both the sort of easy removability offered by Gamvar, and at the same time the strength, protection, and other benefits of the polyurethane.

This system would allow for easier removability than most of the usual removable solvent-based varnishing systems, which require stronger solvents. (Easier according to the usual terms, at least, or of the usual sort in this context -- there are, in addition, other quite valid forms of 'easy' that depend on individual artists, clients, owners, and situations.)

This coating system also means milder solvent exposure; and it is removable with Gamsol OMS, which is milder or less toxic than other OMS products, and the solvents that are used with the other solvent-based varnishes.

***
This approach might sound, at first, as if it is too complex -- as if you are double varnishing. But it is actually just as simple as as the usual application of an isolation coat plus varnish. In this case, the isolation coat is polyurethane. There are no additional steps or complexities -- it is basically the same process.

There is additional information about Gamvar in this PDF:

http://www.gamblincolors.com/newslet...Varnishing.pdf

***
Other removable varnishes can be used in the same way, and different artists will have different preferences. I doublechecked and confirmed the compatibility issue with Golden (and also intend to double check and confirm the compatibility issue with Gamblin).

***
There are additional approaches, but I am low on time here, and the above are the clearest and most direct and familiar.

***
A couple of notes on cross-linking: chemists tend to think of cross-linking as occurring between molecules (or between sites on molecular chains), rather than between layers, and it is in this sense that I was using the term. I don't have time to go into that topic in detail here, and it is something of a side-topic, for me at least. There are papers and articles in the art conservation literature on cross-linking. It is a recognized 'problem' with acrylic varnishes. The chemists at Winsor and Newton addressed it, and apparently succeeded in formulating a removable varnish (Conserv-Art) that maintains easier (according to the usual criteria at least) removability for longer periods of time than most other varnishes, and this might be preferable to some people.

http://www.winsornewton.com/products...&ProductID=845

***
Some polyurethanes are much better than others when it comes to the rate and severity of yellowing or ambering (or resisting yellowing or ambering). So if you plan to try polyurethanes, and are concerned about yellowing or ambering, it would be good to make a careful product choice. The manufacturer may be able to provide test data.

Sherwin Williams has a polyurethane product that passed the ASTM 5000-hour accelerated weathering test criteria. I am still trying to find out more.

***
I would like to focus on finding appropriate polyurethane products, and on moving forward with trying them.

If anyone else comes up with test results or other good information on any of these polyurethane coatings, please post.

Last edited by Nilesh : 07-02-2010 at 08:49 PM.
 


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