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Monday, July 29, 2013

Painting on Panel: Oil Priming


For those of you that purchase our museum quality panels, Aquabord™, Encausticbord™, Pastelbord™, Gessobord™ or Claybord, we complete the sealing and priming for you on the front of the panel.  However, for anyone who is choosing to do their own sizing and priming for oil painting, these instructions for priming in oil will be helpful.  Our Hardbord panel and the Unprimed Basswood Artist Panel both require sealing and priming before use.

All wood panels must be sealed (also known as sizing) before painting in order to put a barrier between the naturally occurring chemicals in wood and the painting ground. Support Induced Discoloration (SID) occurs when a panel is not properly prepared and these chemicals leach through to the paint on the surface. By choosing a denser panel with a low acid content, an artist greatly reduces their risk of SID. However, all wood panels should be sized (sealed) and primed before painting to ensure their longevity. 


Gamblin® Oil Painting Ground is our first choice in a good quality oil primer. However, the following instructions are virtually interchangeable with a number of other oil painting grounds if there’s one you like better or have more readily available. Gamblin® Oil Painting ground contains an alkyd resin vehicle that allows it to dry within a matter of hours. A number of other pre-made oil primers are also available and generally, they are made up of a white pigment, linseed oil and driers or solvents. Primers that use alkyd resin binder instead of linseed oil dry faster and are non-yellowing and more flexible than traditional grounds. Both may be applied in the same manner with either a large putty knife or a large stiff bristle brush. If you are using a traditional oil primer, it may need to be thinned with Gamsol® to a workable consistency enabling easy application over the sized panel. Never add oil to a primer. Its leanness must always be preserved.

Step 1 – Size and seal the wood
A size is a thin solution (often a weak glue) that is brushed directly onto a support. Sizing or sealing Ampersand's uncoated panels is recommended to protect against SID. In fact, it is extremely important to properly seal any and all un-primed wood substrates to prevent support-induced discoloration that can cause your paint film to yellow over time. Hardbord™ is manufactured using Aspen fibers, a wood with a very low acid content, but still needs to be sized and sealed. The Natural Wood Panel™ and Unprimed Basswood panels are made with a thick basswood plywood top that has been sanded ultra-smooth. They are both seamless and knot-free and provide a perfectly smooth and uniform painting finish. When you apply the size and primer to the basswood surface, you won’t experience the raised wood grain fibers that can happen with some other rougher types of plywood; the surface stays nice and smooth. The basswood panels have solid wood cradles and braces that may be more susceptible to moisture and environmental changes than the birch plywood cradles we use on the Hardbord™. Therefore, Ampersand recommends that you prime both the front and back of the Basswood top to ensure long-term stability of the panel.  The best products we have found to seal wood are Golden® GAC100 [2 coats]  and Gamblin® PVA Size [4 coats].

Apply Golden® GAC100 directly to the basswood or hardboard surface with a 2" paintbrush or putty knife. Apply to the front and back if applicable. Allow the GAC100 to dry completely and follow with an additional coat. Do not sand between layers. Before applying oil primer or the painting ground, allow the GAC100 to dry for 1-3 days so that the sealer can coalesce into a uniform film for maximum protection. If you’re using Gamblin® PVA Size, use 4 coats and follow the same application instructions as for the GAC100.

Step 2 – Protect and prepare the cradle
Hardbord™ is available in either a flat 1/8" panel, with a 3/4" cradle, or with the 2" DEEP cradle. The Natural Wood and Unprimed Basswood panels are available in both a 7/8" cradle and 1.5" cradle profile. You have the choice of painting all the way around the cradle or leaving the natural wood showing for framing purposes. Be sure to size and seal the bare wood if you want to paint completely around the edges of the cradle. Or, to protect the wood from paint and primer, cover the sides of the panel with painter’s tape up to the edge of the surface. Do not remove the tape until the painting is finished. Painter’s tape does not leave a sticky residue like many household masking tapes that can be difficult to remove, and will leave a pristine surface underneath when the painting is complete. 

Step 3 – Apply the Oil Painting Ground or Oil Primer
Begin by mixing small amounts of Gamsol® with the primer to thin if necessary. You can test the right consistency by picking up the paint with a knife and shaking it gently. If it falls from the knife like soft butter, it is ready to use.

When priming with a putty knife [or wedge tool], begin by placing a portion of the oil painting ground or primer in the center of the [already sized] panel. Spread it in one direction, and then in the opposite, and finally in a diagonal direction. Clean the putty knife and run it over the ground to smooth and even out the surface. Also, prime the edges of the panel and the cradles if applicable. Don’t forget to apply GAC100 on the cradle edges first if priming them for painting. 

When the first coat of oil painting ground is completely dry (about 7 hours), lightly sand the surface with a sanding block using light grade 400/grit sandpaper. A second coat can be applied the next day or any time after the first coat is dry. If using basswood, for each additional coat to the panel face, apply the same number of applications to the panel back.

If priming with a brush, use a large bristle brush, at least 2"-3" wide (proportionate to the size panel you are using), and apply the ground or primer with quick alternating strokes, working it well into the surface. After evenly distributing the ground or primer over the entire surface, finish by going over it lightly with a clean brush, carefully in straight lines, or use a short-nap [cotton] roller. Let the first coat dry, then sand and apply a second coat. At least two coats of ground or primer should be applied. The more coats of ground or primer that are applied, the smoother the surface will become. For basswood panels, follow the same instructions, but also prime the back. For each additional coat to the panel face, apply the same number of applications to the panel back

Step 4 – To Finish
Eliminate any unevenness on the finished primed surface by lightly sanding the panel after it has thoroughly dried. The finished primed panels should be allowed to dry completely at room temperature before painting. If you prepare several panels at a time, then you will have stock on hand that is dry and ready to paint when needed. 

Below is a video produced by Gamblin with Scott Gellatly, technical director, explaining how to prime a painting.


All things Ampersand,
Karyn Meyer-Berthel
Artist & Social Media Specialist
Ampersand Art Supply

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