by Jane Sutherland

Extending the Drying Time of Acrylic Paint
Can you suggest products and techniques to extend the blending time of acrylic? I have tried a number of mediums, but they add gloss to my painting and are overly viscous.

Moderation is the key to using mediums that extend the drying time of acrylic paint. One of the newer mediums that delay the drying time of acrylic is a glazing liquid, which is part acrylic dispersion medium and part retarder. There are two ways to use the glazing liquid: You can apply it directly to the painting ground, thereby effectively glazing the ground. This slows the drying time of unmodified paints applied on top of the ground to about 45 minutes. Or you can mix a moderate amount of the glazing liquid directly into the paint. Be aware that the more glazing liquid you add to the paint, the more transparent it becomes.

Another medium that delays the drying time of acrylic is an acrylic retarder gel. Spare amounts of this jellylike substance can be added directly to acrylic paint. Be cautious with additions of retarder because too much of it can prevent the paint film from drying thoroughly and cause it to weaken. When selecting these mediums it is usually a good idea to stick with the brand of paint you are using rather than indiscriminately mixing media. A simple way to extend the blending time of acrylic paint without using a medium is to moisten the paint with a fine spray of water as you work. An ordinary household plastic spray bottle works well for this.

Read more Technical Q&A features.

How to Seal Acrylic Paintings
What do you recommend for sealing acrylic paintings on canvas, wood, or glass? In the past I used a clear polycrylic spray but it has caused the painting to yellow.

Polycrylic spray is not intended for use with acrylic paintings on canvas, wood, or glass. Similar to polyurethane products, it was developed for industrial purposes to seal furniture, cabinets, flooring, boats, and the like. A lacquer coating is sometimes used for artistic purposes but tends to yellow with age and may crack or have problems adhering.

Acrylic solution varnish, preferably with ultraviolet light protection (UVLS), is the best type of sealer for acrylic paintings on canvas, wood, or glass. This varnish is available in matte and gloss finish. You can also seal an acrylic painting with a coat of acrylic gloss medium followed by a coat of a solution varnish for additional protection. This second coat of solution varnish is necessary because the gloss medium alone is as vulnerable as the paint film.

Removing Varnish From an Oil Painting
How do you remove varnish from a finished oil painting to redo an area that you are not satisfied with?

Of the two main types of varnishes, solution varnish and cooked-oil varnish, theoretically a solution varnish (a resin dissolved in its solvent) is supposed to be reversible with the original solvent. Unfortunately, this is not always true. Even if it were true, the job of removing a varnish film from an oil painting is best left to a trained restorer.

To successfully remove varnish, it is necessary to know exactly what type of varnish was used in order to choose the right solvent. The painting must have dried for 12 to 18 months before the varnish was added or else the solvent may lift off some of the paint. It is important to work in a controlled atmosphere completely free of dust and with good ventilation because when lifting varnish the surface becomes extremely tacky and attracts dust particles, fine hairs, and any impurities in the air.

Given that it is your own painting, it is understandable that you may wish to take off the varnish yourself, rather than bring it to a conservator. Even so, a better use of your time would be to set the painting aside and paint another one, which will be fresher and more informed.

Prepared Canvases
What is the difference between oil-prepared canvas and chalk-prepared canvas?

Oil-prepared canvas is made for use with oil-painting media only. This type of canvas is primed with two layers of linseed oil-based paint. Chalk-prepared canvas, primed with two layers of powdered chalk-based paint, is for use with tempera paint. Such specialty-type prepared canvas is generally made of the highest quality linen or cotton and is available in select fine art-supply stores. The universal-type canvas intended for all kinds of paint, including acrylic, is prepared with two layers of titanium white primer plus an acrylic binder. Remember to store stretched canvases back-to-back and front-to-front according to size and keep them in a dry, cool environment.

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