Different mediums to seal hardboard for oil painting?
December 13, 2014 4:44 PM Subscribe
I bought some hardboard for oil painting; I plan to cover it with acrylic gesso. I've been told by an experienced painter to use GAC100 to seal the board to prevent discoloration due to chemicals leaching into the paint from the hardboard. I've read articles that say either GAC100 or high-quality (e.g. Gamblin) PVA. Do you use those, or something else, for this purpose? Will any acrylic polymer substitute?
I have 3/4 of a quart of Daniel Smith matte acrylic medium on hand. I'd like to use it for this purpose, but I don't want to spend the time to do that, paint the painting, and then find out I really, truly should have used GAC, or whatever. Confusingly, the DS label says "this product is formulated with pure acrylic polymers," which is what GAC claims to be, I think.
I have 3/4 of a quart of Daniel Smith matte acrylic medium on hand. I'd like to use it for this purpose, but I don't want to spend the time to do that, paint the painting, and then find out I really, truly should have used GAC, or whatever. Confusingly, the DS label says "this product is formulated with pure acrylic polymers," which is what GAC claims to be, I think.
The Daniel Smith product is fine to use - their mediums are as high quality as Golden's to my mind.
posted by leslies at 6:54 PM on December 13, 2014
posted by leslies at 6:54 PM on December 13, 2014
Response by poster: Thank you, monopas.
leslies, Daniel Smith products have never let me down before, but I'm slightly leery because of the uniform response I've gotten in asking about this elsewhere.
Yes, effluvia, tempered masonite.
posted by cupcakeninja at 7:57 PM on December 13, 2014
leslies, Daniel Smith products have never let me down before, but I'm slightly leery because of the uniform response I've gotten in asking about this elsewhere.
Yes, effluvia, tempered masonite.
posted by cupcakeninja at 7:57 PM on December 13, 2014
Best answer: It's not a matter of the Daniel Smith products not being good, it's just that a matte medium doesn't result in the same sort of film as a product like GAC 100. You can't substitute Golden's matte medium for the GAC 100, either. This page from Golden explains it a little more.
posted by jimw at 8:52 PM on December 13, 2014 [1 favorite]
posted by jimw at 8:52 PM on December 13, 2014 [1 favorite]
Best answer: Untempered masonite that has been tinted dark is most likely to cause problems with the ground bleeding. Tempered masonite is sealed with heat; the ground is sawdust with an artificial wood glue resin. With current resins in use in the industry, the bleeding problem would only be of concern if you work with acrylics in very thin pours with a lot of surfactant or other materials that underbind the paint resin.
Plastic films used for painting range from a glue like PVA to gesso primers with titanium and resin solids to matte mediums which are the acrylic resin without the titanium for opacity. It's a continuum with different market niches for the art materials market, if you take my meaning.
Acrylic primers are formulated slightly more basic in pH to encourage greater drying rate and adhesion for upper surfaces. A bit of tooth or texture is good to also encourage paint adhesion.
The matte medium achieves its matte effect with resin solids for texture, and would probably make a good surface primer--try a test swatch for a textural surface.
The key thing to my mind would be application and drying. Apply your primer in thin coats, and allow it to dry completely. Drying rates will be affected by ambient moisture conditions; dry summer days much faster than cold winter rainy days.
The rigid substrate will be very good for the integrity of your paint film. I think, from an earlier conversation that you are working in acrylic top layers. Acrylic applied in thin layers in traditional painting methods should dry at a uniform rate and not have blooming (color ground bleeding) or adhesion problems as opposed to traditional oils, which dry at very different rates.
posted by effluvia at 9:48 PM on December 13, 2014 [1 favorite]
Plastic films used for painting range from a glue like PVA to gesso primers with titanium and resin solids to matte mediums which are the acrylic resin without the titanium for opacity. It's a continuum with different market niches for the art materials market, if you take my meaning.
Acrylic primers are formulated slightly more basic in pH to encourage greater drying rate and adhesion for upper surfaces. A bit of tooth or texture is good to also encourage paint adhesion.
The matte medium achieves its matte effect with resin solids for texture, and would probably make a good surface primer--try a test swatch for a textural surface.
The key thing to my mind would be application and drying. Apply your primer in thin coats, and allow it to dry completely. Drying rates will be affected by ambient moisture conditions; dry summer days much faster than cold winter rainy days.
The rigid substrate will be very good for the integrity of your paint film. I think, from an earlier conversation that you are working in acrylic top layers. Acrylic applied in thin layers in traditional painting methods should dry at a uniform rate and not have blooming (color ground bleeding) or adhesion problems as opposed to traditional oils, which dry at very different rates.
posted by effluvia at 9:48 PM on December 13, 2014 [1 favorite]
Best answer: Acrylic paint is polymer binder, pigment, and water. As it dries, the binder bonds to the surface and itself so it won't take up water again afterwards - it's basically a dry latex layer. The polymer mix itself is fairly basic and the cheap part of the paint, exact makeup will depend upon the paint maker. While it is itself no longer water soluble once dry, it's not waterproof - water can still leech through.
The problem with painting directly with acrylics on an unprepared surface is that the water can leech pigments directly from the surface, which then get bound up with the polymer and discolour the final finish.
The same applies with oil based paints, where it's the oil that can leech pigments from the surface - and given the drying time of oils, they're more prone to it as there's more time for it to pull up unwanted pigments.
Acrylic mediums are just the polymer binder and water, without the pigment. Matte medium has matting agents added, so that when it dries transparent, it cuts down on direct light reflection, i.e. it's not shiny, which straight binders are prone to. They're all pretty much the same between companies, just different levels of water/polymer mix out the bottle.
Acrylic primers are also acrylic medium, but with additional agents added to bind better to the underlying surface, give a bit of tooth for the next layer, potentially stiffen the underlying surface, and depending upon the primer, they can also provide a better waterproof layer to prevent water or oil seeping through to lower layers and leeching pigment.
So, to actually answer the question; matte medium in and of itself (or other straight polymer binder), is not enough to completely seal off the surface from subsequent layers, any more than normal acrylic paint would. It's designed to cut down on gloss reflections, either in its own layer or mixed in with other acrylic paint. It's also useful when thinning acrylic paint with a lot of water; extra binder helps the original pigment dry evenly without changing the colour.
Acrylic gesso (which itself uses a polymer binder) when used for oil painting is a form of primer, that's used to provide a good toothy surface for oil paint to grip onto, and provide an even solid colour as a base; but is more porous than straight acrylic, thus the suggestion to put a sub-primer.
You will probably get away with it if you wash the board down with alcohol first to clean it, then use two or three layers of matte medium to provide a base and somewhat protect the gesso, and then a couple layers of gesso, possibly sanding between layers to improve mechanical tooth. Those extra layers will definitely help seal off the surface somewhat, and modern hardboard is supposedly much better these days.
But primer specifically designed to seal off the surface and prevent leeching, such as GAC100, would be the best choice, and probably worth getting if this is a painting you're going to care about.
posted by ArkhanJG at 12:03 AM on December 14, 2014
The problem with painting directly with acrylics on an unprepared surface is that the water can leech pigments directly from the surface, which then get bound up with the polymer and discolour the final finish.
The same applies with oil based paints, where it's the oil that can leech pigments from the surface - and given the drying time of oils, they're more prone to it as there's more time for it to pull up unwanted pigments.
Acrylic mediums are just the polymer binder and water, without the pigment. Matte medium has matting agents added, so that when it dries transparent, it cuts down on direct light reflection, i.e. it's not shiny, which straight binders are prone to. They're all pretty much the same between companies, just different levels of water/polymer mix out the bottle.
Acrylic primers are also acrylic medium, but with additional agents added to bind better to the underlying surface, give a bit of tooth for the next layer, potentially stiffen the underlying surface, and depending upon the primer, they can also provide a better waterproof layer to prevent water or oil seeping through to lower layers and leeching pigment.
So, to actually answer the question; matte medium in and of itself (or other straight polymer binder), is not enough to completely seal off the surface from subsequent layers, any more than normal acrylic paint would. It's designed to cut down on gloss reflections, either in its own layer or mixed in with other acrylic paint. It's also useful when thinning acrylic paint with a lot of water; extra binder helps the original pigment dry evenly without changing the colour.
Acrylic gesso (which itself uses a polymer binder) when used for oil painting is a form of primer, that's used to provide a good toothy surface for oil paint to grip onto, and provide an even solid colour as a base; but is more porous than straight acrylic, thus the suggestion to put a sub-primer.
You will probably get away with it if you wash the board down with alcohol first to clean it, then use two or three layers of matte medium to provide a base and somewhat protect the gesso, and then a couple layers of gesso, possibly sanding between layers to improve mechanical tooth. Those extra layers will definitely help seal off the surface somewhat, and modern hardboard is supposedly much better these days.
But primer specifically designed to seal off the surface and prevent leeching, such as GAC100, would be the best choice, and probably worth getting if this is a painting you're going to care about.
posted by ArkhanJG at 12:03 AM on December 14, 2014
Akk, forget to say that you should let each of the primer layers dry completely before adding another layer, whether you use matte medium or a proper primer.
posted by ArkhanJG at 12:10 AM on December 14, 2014
posted by ArkhanJG at 12:10 AM on December 14, 2014
Hi, I had to giggle, my Dad has been painting on wood since the fifties. Doors, scraps, plywood, etc.
Weirdly enough he used latex house paint to prepare his surfaces. I suspect he'd use Kilz or Zinsser 1-2-3 these days. He used latex house paint to paint them too. He was covering HUGE areas so economy made a big difference to him.
If using oil paints, use an oil based primer, but I don't think you need to use a high-priced, special arty primer if what you can get at Home Depot for $20 per gallon will do.
Every painting he's done is still alive and kicking, and he'll even touch them up periodically if they look scuffy.
YMMV, and you may be a different kind of artist than my Dad, who mostly painted for fun (although everyone we know loves his work.)
posted by Ruthless Bunny at 5:50 AM on December 14, 2014
Weirdly enough he used latex house paint to prepare his surfaces. I suspect he'd use Kilz or Zinsser 1-2-3 these days. He used latex house paint to paint them too. He was covering HUGE areas so economy made a big difference to him.
If using oil paints, use an oil based primer, but I don't think you need to use a high-priced, special arty primer if what you can get at Home Depot for $20 per gallon will do.
Every painting he's done is still alive and kicking, and he'll even touch them up periodically if they look scuffy.
YMMV, and you may be a different kind of artist than my Dad, who mostly painted for fun (although everyone we know loves his work.)
posted by Ruthless Bunny at 5:50 AM on December 14, 2014
Response by poster: Thank you, all. These answer my question. effluvia, you've given me a lot to consider (again!), and ArkhanJG, I appreciate the nuanced polymer/binder discussion.
posted by cupcakeninja at 2:27 PM on December 14, 2014
posted by cupcakeninja at 2:27 PM on December 14, 2014
This thread is closed to new comments.
And if I was going to put as much time as you probably will into your painting, I'd get the support as right as I could. But I am extra cautious. Whatever you do, have fun.
posted by monopas at 5:11 PM on December 13, 2014