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Monday, January 20, 2014

Spraying

    One important but highly overlooked part of canvas print is the spray coat. It protects the print from damage during stretching and over the course of its lifetime. If done correctly it goes unnoticed, but if done incorrectly it can highly degrade the visual appeal of your print. The modern standard and most effective tool to use for spraying is a High Volume Low Pressure Spray Gun (HPLV). Following the steps explained below will help you achieve a high quality finish that will protect your piece and will add to its appearance.

    A number of varnishes come with too high of a viscosity to be sprayed and must be watered down. The traditional method of determining the right ratio of varnish to water is trial and error, however, there is an alternative. One can use an instrument called a Zahn Cup, which gives the time that it takes a standard amount of liquid (40cc) to flow out of a opening at the bottom. We recommend that if you choose to use a Zahn Cup to determine the right mixture that you shoot for a time from 24-25 seconds. It is important to make sure that you do the test for the Zahn Cup at the temperature as you do your spraying, higher temperatures increase the viscosity of a substance. Using this method eliminates the need for trial and error and can give a more standardized estimate for the correct ration. 

    After verifying that the varnish is of the right viscosity the next step is setting up your surroundings. The print should be in a well-lit area so that all the varnish is visible when sprayed and any blemishes easily seen and the spray hits evenly from all directions hit in the same place. If it is angled incorrectly then it will accumulate more thickly in one portion and leave a line on the print. Having a location where the print can dry safely after being sprayed is also something to consider. Spraying in a busy studio where it is likely to be hit or moved prior to drying is not the best location.

    Once you have your varnish mixture and location set up, the next step is determining the prior spraying distance and angle. We usually stand where the spray gun is approximately 12-14 inches from the canvas, this gives a nice even coating without being too thick, and a psi range that allows an even coating. The strength of different guns varies at psi ranges so there is no set psi, just find whatever pressure gives you a nice, even coating on your canvas.

    A technique that we have found effective at reducing overlap in coats is to use a different number of passes in every coat. Lets say you were putting on a coat from left to right and the first coat you used 8 passes, the next one you would use a number of passes such as 6 or 10. This spreads out the edges of each pass so that they don’t all end up in the same area and increases consistency.

    We recommend going with multiple thinner coats, rather then one or two thick coats, the reason for this is it reduces room for error. When a thick coat is applied to a canvas it has a much higher chance of running and creating blemishes, while a thinner coat does not have this problem. Matte canvas prints require more coats then a comparable glossy canvas and this should also be accounted for. A larger number of thinner coats also allows for a more precise finish, when you reach your desired appearance you simply stop there.

    Following these simple steps can help you properly coat your finished canvas prints and prepare them to be professionally framed and displayed.