JUST PAINT Published by GOLDEN Artist Colors, Inc. / Issue 3 Dry Notes on Drying! Understanding How to Control the Drying Process of Acrylics Acrylic waterborne paints tend to dry extremely quickly. This is not earth shaking news for anyone who has explored acrylic paints. For some, this is the Acrylics greatest advantage and for others its greatest weakness. Several techniques and additives can extend wet time on the palette, on the surface, on the tools and even in the containers. In this article, we will review the mechanism of drying of acrylic paint and how that process can be controlled and manipulated to an artist’s advantage. Paint Drys As Water Evaporates Waterbased acrylics dry as the vehicle that carries them -- mostly water -- evaporates. As water evaporates, or is Thickly applying gels or watering down mediums can lead to stresses absorbed by the substrate (canvas, paper, within the film causing crazing upon drying gesso, etc.), the microscopic acrylic polymers, which are shaped like spheres, are forced into ever closer contact. point, but the paint no longer flows easily. longer sufficient water to keep the acrylic Eventually they’re crowded so tightly that Another indication is that the brush begins polymer from forming a film. For very the spaces between them create capillary- to drag over the surface. The paint doesn’t thin films this could occur within minutes, forces, and water is actually pulled from seem dry, yet it is difficult to move and while the time for thick films to skin over the paint film. This capillary action packs fairly sticky. This is often a point where may be a full day. the acrylic spheres against one another in a overworking the acrylic will cause the The third stage of drying is the honeycomb-like pattern, and permanent clouding of glazes or time required for the entire thickness of clear coats. This stage is marked the film to be thoroughly dry. That is they begin to form a more or ▲ less continuous, cohesive film. physically in the paint film by a when the remaining water and solvent As this occurs, the polymer PAINT DRIES dramatic reduction in water (used as freeze-thaw stabilizer and IN 3 DIFFERENT spheres deform and partially content at the surface. However, coalescent) evaporate and leave the film. STAGES. since evaporation is still This is a most crucial time frame to be combine with one another in a DRYING TIMES process of film formation called SHOULD BE occurring very quickly from aware of as the ultimate physical proper- coalescence. THOUGHT OF layers below, no film formation ties, such as adhesion, hardness and clarity, Three stages of drying IN SEVERAL has yet taken place. In very thin do not fully develop until the film is near DIFFERENT TIME paint films this can occur within complete dryness. For very thin films, this Paint actually dries in FRAMES. seconds. time may be a few days, while films of 1/4 three very different stages, ▼ In the second stage of inch thickness or more will take months hence drying times should be drying the paint actually forms a and up to a year to be completely dry. thought of in several different skin over the surface. This is the time frames. The first stage results in the Moving Artwork time when people frequently judge the formation of a semi-dry surface. No film Many artists are not aware of this paint as, “dry to the touch”. There is no formation has actually occurred at this sometimes lengthy drying time. Often Continued next page... Just Paint / Issue 3 2 Continued from Front... cases treatment in a desiccant cabinet with temperature and humidity conditions. Drying Notes reduced humidity may be necessary.) Practical Considerations: paintings can be ruined if painted Environmental Considerations There are no limitations for very thickly and moved during this period Environmental factors that regulate applying additional acrylic paint. That is, of drying. In very thick paintings, three the evaporation of water also influence the you can apply acrylic paints while the weeks is a minimum before moving the drying times of acrylic paint films. These underpainting is still wet, just skinned work, as cracking may include: temperature, over, or has dried for several years. (If occur within the region humidity and airflow. painting over an old acrylic surface, be sure of the film not thor- Temperatures below to clean off any accumulated dirt or oughly coalesced. Until 49oF (9oC) will not grime). If you are going to apply oils over complete coalescence or allow the acrylic the acrylic underpainting, wait until the film formation has been polymer solids to acrylics are completely dry. achieved, the paint will properly coalesce to For varnishing, it is also best to wait not reach its optimum form a continuous film, until the painting is completely dry. performance in adhesion, and may result in film Trapping excessive levels of water and/or durability or block failure (cracking, solvent, may result in clouding or poor resistance (reduced tack adhesion failure, initial adhesion of the varnish. This is more of the surface). Addition- powdered film, etc.). important when the varnish forms a tight, ally, clear films of gels, Relative humidities in low-permeable film, such as in the case of clear mediums, or lightly excess of 75% will slow GOLDEN MSA Varnish. When a top coat colored glazes will not the evaporation of is more open, or permeable, such as an reach total clarity until water from the surface, isolation coat of GOLDEN Soft Gel, the completely dry. slowing the drying degree of drying is less crucial. When using Blanching or clouding process. While a GOLDEN Polymer Varnish, which is a may occur in works that moderate and steady waterborne product, the paint film must have appeared clear, and airflow in the drying also be completely dry underneath. are then stored away in a area is favorable for Applying this varnish over drying paint may damp basement or on thorough drying, a result in tackiness, clouding or even top of each other. These strong breeze, especially cracking. films may not have been one directly on the Controlling Drying Time: thoroughly dry, or the paint surface, can cause Depending on the objectives and storage conditions film formation failure, techniques, artists have varying needs to caused them to trap such as cracking and/or keep paint from drying too quickly. They moisture. Given enough wrinkling. Tempera- may require longer mixing time on the time for more complete drying, clarity, tures of 70 to 85oF and humidities under adhesion, block resistance and hardness 75% are ideal. Yet acrylics have been very may improve dramatically. (In very severe successfully painted within a wide range of Continued page five... ABSTRACT Study Reveals Causes for ‘Support Induced Discoloration’ by Mark Golden, President Jim Hayes, Technical Director Ben Gavett, Assistant Technical Director This study was conducted by Support Induced Discoloration (SID) is more evident in thicker, more transparent applications. Golden Artist Colors, Inc. and Buffalo State University Department induced discoloration” (SID), comes translucent acrylic mediums. of Conservation. The researchers at from the water soluble components This paper, available from Golden had uncovered a phenomena in unwashed canvas, linen, and Golden, is the reprint from the of discoloration previously not masonite. The effect is particularly 1991 symposium “Saving the described within the literature. This evident in very transparent glazes or Twentieth Century, The Conservation discoloration, coined “support thick applications of transparent and of Modern Materials”, held in Canada. GOlDEN ARTIST COLORS Just Paint Most waste is disposed of into avoid disposal of these by purchasing Glamour, Fame either the water, ground, or air. only what will be entirely used. The United States Environmental • Before using water to clean palettes, and Fortune Protection Agency, state agencies, brushes, containers and other tools, and local authorities all have wipe them with a paper towel and Available regulations affecting such disposal. allow it to dry before disposal. This Questions are best addressed to makes the wash water stay cleaner Without Effort the local facility first, such as the longer and keeps paint solids from landfill or water treatment plant.1 going down the drain. or Sacrifice! Questions about whether or not a • Solids in washwater can be further Please don’t be disappointed, material is considered a “hazard- minimized by removing them with a simple treatment process. See the ous waste” and the best method but this article is really about the other side for further information on for its disposal, can also be di- best alternatives for disposing of treatment process. wastes generated while painting. rected to the manufacturer. I know it is a lousy trick, but the TIPS TO Editor insists on captivating TIPS ON BEST headlines. However, there are real DISPOSAL REDUCE WASTE benefits to doing a good job with • Purchase products in the optimal PRACTICES container size. Buying too small results waste management practices, and in more packaging wastes. Buy too if you stay till the end of the • Even with water-based products, it is best to discard a solid instead of much, and you risk having more than article, you may come away with washing everything down the drain. can be used or having the product fail some Also, liquid paint should not be taken during storage. new ideas. - Ben Gavett to a landfill. If allowed to dry, film- • Use work practices that minimize forming paints such as acrylics lock wasted paint. For acrylics, try a There are a few generalizations pigments in place and help prevent moisturizing palette and keep the about waste disposal that are them from moving around in the paint covered as much as possible.