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  • Remedying overextended acrylicsApproveRejectUn-ApproveSubscribeUn-Unsubscribe
    Question asked 2017-04-09 12:32:20 ... Most recent comment 2017-04-11 20:18:00
    Acrylic Paint Additives Art Conservation Topics
    Question

    I know that acrylics can be made less durable by adding too much water or extender/retarder to them. I was wondering if this could be remedied later on by either

    a) coating the weakened layer with medium

    b) overpainting the weakened layer with acrylics that haven't been overextended or oils

    ?

    Would sealing the overextended layer with medium/paint have a similar protective effect as painting over tempera with oil?

Answers and Comments
  • EditDeleteModerator Answer

    We are sending this question to a few of our moderators who are more directly involved in acrylic dispersion media but I will attempt to provide a preliminary response. First, I do need to ask what you mean by too much extender. Are you adding additional clear acrylic dispersion medium to the paint? If that is the case, you are not really diminishing the binder and the paint film should remain resilient. If you mean adding a dry powder like chalk or additional pigments to the paint, you are in essence raising the pigment load and weakening the binding strength.

     

    First, to my mind, I think that we need to separate the issues of acrylic dispersion paints that are thinned with too much water with that of adding too much retarder. The first is a physical alteration while the second is also chemical. I cannot really comment on the latter and we will have to wait for someone with greater expertise in this area.

     

    I do think that applying a thin dilute layer of acrylic medium over the underbound paint could help to stabilize the layer. Generally, applying a fatter paint layer over an overly lean layer does not always solve the problem, this is certainly true of oil paint, but even in that circumstance there are times when it is helpful. To be clear, though, one should never apply straight oil over a layer of oil paint unless this area will receive subsequent layers of pigmented paint (see our “Varnishes” document in our RESOURCES section for more information about “Oiling out”). The use of clear surface applications of medium is far safer in acrylic dispersion paints where the yellowing of the binder is relatively insignificant.

     

    The answer to “b” is likely similar but I will leave this to those more experienced in acrylic dispersion paints. Probably the medium heavy application of additional acrylic dispersion paints would work. The efficacy of the superimposition of oil paint would depend upon the degree of stability of the lower acrylic dispersion paint layers. Likely, a lean acrylic underlayer would function similarly to a lean acrylic ground and the results would be satisfactory. An extremely underbound layer, however, may be so thirsty for medium, or so friable, that either the top layer of paint is drained of its binder or the adhesion to the lower layers is compromised. Again, others may be able to provide a more precise answer.

    Brian Baade
    2017-04-09 14:20:28
  • EditDeleteModerator Answer

    Hi -

    Similar to Brian's reply we would want to understand what you mean by "over extended" in terms of water. This is especially true as this is an area that is likely in our top 5 misunderstandings, at least in regard to our acrylics and likely other professional brands. In terms of Golden acrylics, our standard Heavy Body and Fluid acrylics can easily be thinned by up to 1:1 with water while still producing a very durable film. And in fact in many tests on Plexiglass - a very nonabsorbent surface - we still had good adhesion at ratios of 1:2 and 1:3 paint to water ratios. So acrylics can take a lot of thinning and still be fine. And then too a lot depends on the conditions of application. For example, dilute a tablespoon of acrylic paint in a gallon of water, then let evaporate, and you will find that you still end up with a fine acrylic film at the bottom of the bucket! The reason being that the initial dilution is still quite contained in area.

    As for your concerns, if worried you went too far in thinning, one quick test would be to rub an area lightly with a wetted Q-tip and see if there is color lift or an obvious powdery surface. If yes, or if just wanting to play it safe, you can carefully apply a layer of an acrylic medium over the surface and that will fully consolidate and lock in the area and allow you to freely apply more acrylics or oil paints on top. In the case of oils, however, we would recommend something like our Fluid Matte Medium as a form of 'clear gesso' that will provide adequate tooth and adhesion for oils.

    And if misunderstanding your concerns somehow, or you have further questions, just let us know.

    Hope this helps!

    Sarah Sands

    Senior Technical Specialist

    Golden Artist Colors 


    Sarah Sands, Senior Technical Specialist, Golden Artist Colors
    2017-04-09 15:54:08
  • EditDeleteModerator Answer

    ​First, it's important to understand the difference between "retarder" and "extender". Acrylic mediums that are sold as "extenders" contain the same polymer dispersion base as acrylic colors, so adding a lot of medium doesn't result in a weaker film. Alternately, most retarders for acrylic paint are not acrylic mediums; they are mixtures of propylene glycol, water and gelling agents. Glycols act as coalescents in acrylics, moderating the rate as which the film forms and achieves full integrity. Adding extra glycol and water-gel keeps paint wet longer, which is advantageous when painting outdoors on a hot, dry day, or when more suave blending is desired. Since retarders don't usually contain any acrylic dispersion base, they don't reinforce film strength the way acrylic mediums do, so use of the minimum effective amount is recommended. Excessive use of retarder (with our product, more than 25% by volume) can result in a porous film that stays sticky for a long time, and which permanently becomes tacky in warm display/storage conditions. Professional-grade artists' acrylics can be thinned with quite a lot of water and still achieve a durable film, but I have seen really watery, thin applications that don't adhere well. Thinning with a lot of plain water also temporarily lightens mixtures, making it hard to judge the final appearance from palette to canvas. Low-viscosity mediums (e.g. Acrylic Sizing and some of the GAC mediums) added to thinned paint can boost adhesive power, plus help reduce the difference in appearance between wet and dry colors.

    Matthew Kinsey Utrecht Art Supplies

    2017-04-09 17:02:10
  • EditDeleteModerator Answer

    Just wanted to concur with Matthew Kinsey, from Utrecht, about the distinction between a retarder and an extender/medium, ​an issue I really did not address earlier. As Matthew pointed out, putting an excessive amount of Retarder into a paint film - with our products, we recommend no more that 15% Retarder - can result in a persistently sticky, water-sensitive film. Assuming that you do not have that problem, and the film feels fully dry to the touch, we would still recommend testing for water-sensitivity just to be safe. Especially if you suspect that you went well beyond the maximum recommendations of the various brands. To do this, as mentioned before, just use a wetted cotton swab and rub slightly, looking for color lift. If nothing comes up, you are likely fine. If you get staining, then carefully applying a light coating of an acrylic medium of some sort should seal it in. If you get excessive color lift, or have a powdery surface, then you might need to first consolidate and lock down the surface with a light spray of something similar to our Archival Varnish aerosol, and then follow with an acrylic once allowed to dry for 24hr.

    Hope that helps  -

    Sarah Sands
    Senior Technical Specialist
    Golden Artist Colors

    Sarah Sands, Senior Technical Specialist, Golden Artist Colors
    2017-04-09 17:43:20
  • ApproveRejectUn-ApproveUser Comment

    Hello,

    thank you for replies, everyone.

    My main concern was about paint treated with a lot of retarder. The idea was to deliberately add "too much" (50% or more by volume) retarder and brush the mix all over the painted surface in order to get a smooth wet-into-wet blend when I lay down acrylic paints onto it. I would mix a safe amount of retarder into the actual acrylics going on top.

    I am usually incapable of getting acrylics to have the quality of oils when it comes to painting, so one advice I read was to first coat the support with a layer of retarder. What I'm wondering is if it would make a difference if that preparatory layer was tinted.

    2017-04-10 15:59:56
  • EditDeleteModerator Answer

    ​Based on Matthew and Sarah's comments above as well as my own understanding of retarders I would be inclined not to lay down an initial layer of retarder and/or add too much retarder in general. I think they have already outlined some of these issues but I would reiterate that even if a layer of retarder is below an acrylic layer with an appropriate amount of retarder, the lower layer could very well effect the integrity of ANY of the films above it....if the retarder has nothing to "retard" then any subsequent layers on top may have a hard life in the future. But perhaps this is what you are going for? You can certainly experiment but I would consider what folks have stated here....if you do decide to go that route it would be great to record your technique/materials on the back of the painting, not just for future preservation but for yourself as well, to help keep a record in case future problems should arise (or even if everything works out). 

    Kristin deGhetaldi
    2017-04-10 16:14:38
  • ApproveRejectUn-ApproveUser Comment

    I see. I was under the impression that a layer of retarder coated with acrylics would simply mix and end up being about the same as a layer of acrylics with retarder mixed in. Without such a layer to paint into, I find that the acrylics stay on the spot they've been applied to, and any sort of mixing just smears the stroke's upper layer while still leaving a sharp-edged mark where the initial stroke was applied, without the mobility I would like (or that I can get with oils).​

    2017-04-11 12:02:15
  • EditDeleteModerator Answer

    ​Are you avoiding using oils for any particular reason? Perhaps for health concerns?

    Kristin deGhetaldi
    2017-04-11 13:16:18
  • ApproveRejectUn-ApproveUser Comment

    ​I'm avoiding oils mostly due to these four issues:

    1) Health concerns. I don't use anything labelled as toxic or harmful, but I know that my drying oil had a drier added to it. The manufacturer doesn't need to indicate it (due to the amount being small), but it's still there. If I were to touch the painting with my hand, I would worry if I can completely remove the oil afterwards. I don't know if this particular drier (a manganese salt) would bioaccumulate.

    2) They dry too slowly. Having to wait up to two weeks for a layer to finally dry before I can start painting on top is not enjoyable. I could try painting into a tacky layer, but more often than not I would just be making the colors muddy.

    3) They are messy - this relates to the previous issue. I don't have a special oil painting studio, so that means evey time I accidentally touch a brush to anything (like furniture), I have to avoid touching it with anything else to stop the paint spreading everywhere and remember to clean it with solvent.

    4) They are a pain when it comes to maintenance - related to issues number 1, 2 and 3. If I want to avoid both making a mess and ingesting potentially toxic substances, I need to not only wear gloves and be extra careful to not spill anything - I also need to be careful to clean anything that was spilled, and also to avoid contact with the brushes/palette while cleaning. The cleaning, again, involves solvent, and thus fussing with bottle caps on top of taking care not to spill anything out of the sink.

    If there was some way of working with oils without the terrible, potentially toxic mess, I would have gone for it. As it stands, acrylic paint on a support coated with a layer of polyethylene glycol diluted with water 1:2 seems to be the best approximation.

    2017-04-11 19:04:21
  • EditDeleteModerator Answer

    ​Well if not for number 3 we might be able to offer some tips regarding the other issues. It is of course possible to paint without solvent....it just takes some getting used to. As far as driers go, unless you are using solvents and getting paint (with solvent) on your hands, there is very, VERY little chance that such materials would transfer through the skin. Same with oil paints containing lead, cadmium, cobalt, etc. Of course you can always wear gloves. But it sounds like acrylic is something that helps you to ease your worries so there is no problem with that. Many of us have already stated above our concerns about painting over a layer that is rich in retarded so as long as you are aware of the risks I would just encourage you to record your materials and techique on the back of your painting for future reference.

    Kristin deGhetaldi
    2017-04-11 20:18:54
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