Painting Matters #2: Sealing a miniature
by Judith Northwood
Remember, your question can be answered here! Just send me an email with any of your painting quandaries or frustrations, and I’ll select from those for future columns.
Q: Help! My miniature turned cloudy when I sprayed it with sealant. How can I prevent that?
A: The easiest answer is to move to Arizona, but that’s not practical for most of us. Fortunately, there are alternatives.
That cloudy finish is called bloom, and it’s caused by moisture being trapped under the sealant, also often called varnish in the fine art world. The two most common causes are paint that’s not fully dry and atmospheric humidity. Paint should ideally be allowed to dry for 24-48 hours before applying sealant of any sort, but you can speed that up by putting the mini under a warm light source for a few hours. It’s more risky, and can make the paint film a little more brittle, but a good sealant protects the paint well enough that it’s usually not an issue.
Sometimes, the bloom will go away, especially if there are any pinhole gaps in the layer of sealant. That can, however, take months, so it’s better to prevent bloom than try to cure it. I’ve heard of people who have eliminated it by spraying again, but that’s never worked for me, so I offer that option for you to consider, just without a personal endorsement on my part.
Preventing bloom is easiest when you’re spraying sealant in a dry environment, thus my quip about Arizona. Most of the time, the moisture that gets trapped beneath the sealant is made up of water molecules that are caught by the sealant as it travels through the air, then covered by more sealant and water. The water will evaporate from the top layer, but it might not manage it very well beneath lower layers. Thin layers have less chance of causing bloom than thick ones because there will more likely be tiny openings in a thin layer that will let water escape. Waiting until a dry day is another possibility for preventing the problem.
Knowing the cause, though, only does so much when you know you live in an area where humidity tends to be high a lot of the time. If you think about condensation on a glass of iced tea, however, you come to another variable you can use to your advantage: condensation is most common when there is a temperature difference. You can reduce your chances of bloom by leaving your mini and the can of sealant out in the area where you intend to spray. Ideally, this would be for a couple of hours, especially with a full can of sealant. Then, when you spray the mini, much less water will attach itself to the droplets of sealant.
The method I’ve chosen for avoiding bloom, though, doesn’t require waiting, either for a dry day or for temperatures to equalize. I use brush-on sealant. As long as the mini is properly dry, I can sit right in my studio and apply the sealant, which is nice when it’s colder than ten below zero or hotter than a sauna outside. This also avoids the risks inherent in using a product that has volatile organic chemicals (VOCs), present in just about every spray-on sealant on the market. My lungs don’t like even small amounts of VOCs, so brush-on sealants are optimal for me on a number of levels.
If you’d like to use brush-on sealants, you can find water-based and solvent-based. The water-based are much easier to work with and don’t require that you have turpentine on-hand for thinning and brush-cleaning. A number of fine art brands make water-based matte sealant (remember many will call it varnish). Most of the time, you’ll thin the product about 50-50 with water. Thin coats are ideal. Like with drying paint, you can leave the mini under a warm light to dry faster. Always use a natural hair brush, as the sealant will flow more easily off of natural hair than synthetics, and there is less of a tendency for brush marks. Cheap sable brushes are great for this. They cover well, but don’t have much of a sharp point, so you get rapid coverage with a minimum of brush strokes. Also, stroke slowly with the brush, and as much as possible in a single direction. This will prevent air bubbles from forming, as will applying as thin a coat as possible. If you get a few, clean your brush with a quick water rinse, dry it pretty well on a paper towel, then gently go over the area where the bubbles formed. The clean brush should sweep away the puddled sealant and lift off the bubbles.
There are a couple of other things to consider when selecting the sealant you want to use. First is the question of durability. Gloss sealants provide more protection than matte, simply because of the matting agent that has to be added to gloss sealant to eliminate the shine. Matting agent interferes with the maximum possible protective surface. Fortunately, you can do a layer of gloss and follow it with a couple of very thin layers of matte. For tips of weapons and other areas likely to get more rubbing, use two layers of gloss before going on to matte.
And then there is the issue of longevity. It doesn’t particularly matter if the mini isn’t one that will likely be used and/or displayed for a long time, but some sealant products can yellow. This is a result of the particular resin in the sealant reacting with oxygen or ultraviolet radiation. I’ve seen it with Future Floor Wax, Testor’s Dullcote, and a wide variety of wood-working finishes (over wood, what would a bit of yellow hurt?). These products aren’t archival, meaning they aren’t meant to remain perfectly clear for a long time-any more than white school glue would be expected to last. Also, the consistent archival status of craft and hobby brand products is open to question. Fine art brands are much more dependable, but you don’t have to take my word for it. You can test for yellowing yourself. Take a sheet of white paper, cover half of it, and spray some sealant on the uncovered half. Place it somewhere that it will get the most intense UV exposure you can manage, then check it again periodically for a month or so. If there is no perceptible difference between the two halves of the sheet of paper, you can bet that there will be very slow to no yellowing in using that container of sealant.
Sealants aren’t the only things affected by UV exposure. The pigments that give paint its color can also fade or change when exposed to UV for a length of time. The easiest way to deal with that is to purchase a sealant that protects against UV radiation. Krylon and Golden have them in spray products, and Golden, Lascaux, and Old Holland do in a brush-on version. The number of brands offering this protection is growing steadily.
Last but not least, one more caveat. All sealants, but most particularly the matte variety, will alter how the paint job beneath is perceived. Gloss sealants tend to intensify the chroma of the colors used, making them appear more vivid. Matte sealants do the opposite, flattening the visual perception of the paint job so that differences in value (dark to light), contrast between hues and the intensity of chroma are reduced. There isn’t any way to avoid this, so the best way to deal with it is to push your paint job a little further than you want the contrasts to appear in the finished version.
Note about products: Liquitex, Golden, Maimeri, Winsor & Newton, Holbein, Lascaux, Chroma, Matisse-Derivan, and Old Holland are all fine art companies making various grades and styles of acrylic paint and offering a variety of archival varnishes. Liquitex and Golden are made in the USA, Winsor & Newton, Lascaux, Maimeri and Old Holland are made in Europe, and Chroma and Matisse-Derivan are based in Australia. Most are distributed fairly widely. Krylon is a US-based spray paint manufacturer that makes a few cross-over archival products into fine arts. Future Floor Wax is just what it sounds, a US-made product for cleaning and protecting no-wax vinyl flooring. Testor’s Dullcote is a hobby product made for scale model hobbyists in the USA, as are the Armory sealers, and both are fairly widely distributed, Testor’s more so than Armory. Games Workshop is UK-based with world-wide distribution. Reaper makes brush-on sealers in the US that may or may not be available elsewhere. Ask at your local store, or check web-based retailers who ship to your area for specific availability.