Acrylic Varnish info

Let me share our perspective on this, especially since we have been one of the originators of the recommendation for the use of an isolation coat and, while we have not worked with Rembrandt’s varnish, we make similar solvent-based acrylic ones as well.

Isolation coats are technically not required before using a varnish, and in fact we feel artists should always weigh the risks and benefits that an isolation coat provides before deciding to use them,. Isolation coats provide two functions: they even out any differences in absorbency, allowing for the varnish layer to go on more evenly, and – most importantly – it protects the underlying paint should the varnish ever get removed. The reason this is important is that there can be a slight color lift from acrylic films during removal, since they are relatively porous, and the solvents involved can soften the surface. For most conservators, when something like this happens, the process becomes highly problematic and can bring things to a halt as a way to limit damage. So, having this clear barrier in between the paint and varnish simply ensures that this is avoided and makes removal much easier.

That said, isolation coats are permanent additions to a final painting and anything that goes wrong during application cannot be easily fixed. So one should never apply an isolation coat to something of importance without having thoroughly practiced it on various test pieces, or older less valuable paintings, to make sure you are comfortable with the process and getting the results you want. And, as Rembrandt rightfully said, these varnishes can certainly be applied directly to an acrylic painting – it simply means that removal, should it ever be needed, would come with some added risk and need to be done with increased care.

We hope this helps.

Hi – Am traveling and unfortunately will not be able to respond until Monday. If you have some paintings you can practice on you can do some testing. We have not worked with those products so can only recommend doing a test to make sure you like the results. As for whether to do an isolation coat or not, that is a personal choice you will need to make. Certainly an isolation coat helps for future conservation but there are also always risks when applying a non removable coating to a finished piece. 
Anyway, will check back in on Monday and can perhaps offer more thoughts.

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Hi again –

Speaking narrowly, I would be very surprised if there were any problems of compatibility if you applied the Talens varnish on top of the Liquitex product. However, the only way to truly know if you will get the results that you like is to practice.  I also always hesitate to encourage someone to learn how to varnish, or to perfect a new process, while working on pieces of any importance. Varnishing like anything else in art, requires skill and experience to do well, but unfortunately by the time we consider doing it, we usually are having an exhibition of pieces that have emotional and financial value. So I truly do not know how to advise you. Applying the Satin Varnish directly might be fine, but we have no experience with these products and so also have nothing to go on. And definitely most varnishes applied directly to acrylic paintings run the risk of color lifting when the varnish is removed.  This is more likely given that the varnish is a solution acrylic containing turpentine as part of its ingredients. These types of varnishes, which includes our own MSA varnish, can crosslink over time and require increasingly stronger solvents to reactivate them. While Isolation Coats can help protect a painting from these problems, we always worry when artists try doing them when rushed and new to the process, and working with an unfamiliar product on top of it. Anything that goes wrong at this level is not repairable. Given all that, there is certainly always the option to simply not varnish at all and realize that the paintings, while vulnerable to surface scratches and dirt, would still be considered durable works of art and be in a similar situation as the vast majority of acrylic paintings which are unvarnished when they are shown.

See my answers below to your questions:The only varnish that I can buy here from Liquitex is Satin Non-Removable Varnish in spray, but I think it is better to apply a removable one? 

Yes, I agree. Removable is better.

I want to ask, if I test this on one small piece of less importance than those that are really important, and apply one coat of Liquitex Gloss Medium/Varnish as isolation and then varnish it with R.Talens Amsterdam Varnish,  how long should I wait to see if it is ok? I mean if something is wrong, will it be shown in a few hours, days, weeks..? 

Any issues should show up quickly. The main things to watch for are bubbles or foam in the isolation coat that do not pop while drying, which you would notice once that layer is dry. Unfortunately, there is no ability to fix this problem if it occurs, although a Satin or Matte Varnish applied on top can sometimes make it visually less noticeable, but not always. In terms of the varnish, the main difficulty with Satin or Matte Varnishes is getting an even application with no sense of blotchiness or streaks. This also is usually noticeable once dry.  If the varnish is in a spray, then an uneven sheen can often be evened out or lessened by simply applying additional light layers. Brushing is more difficult and can take practice. In our experience making sure not to overwork the varnish and applying enough so that the varnish has time to level out is important. 

Is the best way to put isolation coat in one layer and not too thick? And when isolation coat is applied how long should I wait before I put the varnish?  

In general yes, applying one thin layer is best. We would generally say to allow it to dry for one day before applying the varnish.

I can’t emphasize enough that giving recommendations about products I have no experience with is difficult. So test, test, and test again are all we can suggest. If things look fine with each step, then I think you should be okay as problems with these types of products tend to be obvious and show up once fully dry.

Best of luck with your project. Just the fact that you are taking so much care to get as much information as you can tells me that you have a good chance of being successful in your application.