Case in point is the clarity of that “clear” finish you are about to apply over your project. Whether you just stained or didn’t stain (because you wanted the natural wood tones to show), the finish you are about to apply may not be as “clear” as what you had in your mind’s eye. How clear is clear? You may have heard finishes being referred to as “clear,” “water white,” “non-yellowing,” “water clear” or perhaps no distinction has been made at all to the coatings clarity. Are they all the same thing? What differences will they make to our final piece and will they continue to affect the color over time? Does it matter how many coats we put on? Is there a difference in clarity between solvent and waterborne products?

 

The truth of the matter is that finishes exhibit different colors or hues depending on what materials or resins and solvents that goes into them. Some ingredients can cause that coating to change over time or when placed in sunlight and believe it or not some coatings will change color in the absence of light! Depending on the materials used to make up the coating, it could start changing from the moment it is applied and continue to change for several years as it ages.

To keep things simple, let’s look at some of the most common buzz words we hear in coatings talk and shine a light on the true meaning behind the words.

 

Clear can simply mean that it is a transparent coating, many times having nitrocellulose or some kind of oil in its formulation. Some finishes in this category could be polyurethanes and nitrocellulose and some pre-cats. When I hear “clear” I think root beer, for the possible amber effect that will happen.

 

Water White can simply mean that you can see through to the bottom of the can. In many cases the manufacturer has used a coconut alkyd to help lessen the yellowing, however it can still have amber characteristics. Many pre-cats and post catalyzed lacquers now are packaged as water white finishes. I hear and think ginger ale, far less amber in color (than root beer).

 

Non-Yellowing or Water clear these are usually the buzz words used when there is no presence of an ingredient that will cause the coating to yellow. I hear and think 7-Up. Conversion varnishes, most waterborne and acrylics are often found in this category.

 

CAB coatings are made up of cellulose acetate butyrate an ingredient that doesn’t yellow, yet has the technology and ease of nitrocellulose finishes without the yellowing. I hear 7-Up.

 

How does this affect your work? Well let’s say you are looking to do a white wash stain or perhaps you are glazing a painted finish and need to apply a clear finish coat over the glaze to lock it in. You certainly wouldn’t want to top coat that with a finish that exhibits an amber cast or even a ginger ale hue; it would change your color from white to an antique look. If you didn’t already know the true clarity of the top coat it could cost you hours of rework.

 

Keep in mind that sealers also exhibit color changes or hues that must be considered when putting together your finishing system. Every layer of color and finish builds depth, clarity, sheen and final color. It is for this reason that a STORY BOARD (refer article Oct 2010 for more on story boards) should ALWAYS be made when designing your color samples. To assume… well you know what happens when one assumes.

 

Even a non-yellowing finish can change the overall appearance! Take a white sheet of paper and slide it into a clear sheet protector or place a piece of plastic wrap or shrink wrap over it, did the white change in color? Now place on another layer and so on, see the change? This is what you are doing with every coat of finish you apply.

 

Waterborne finishes although clear, do cast a different appearance than the solvent-based coatings and for this reason always be sure to make your story board on how your color will progress using this type of coating. When first applied many times it can be very milky in appearance but then dry clear. Some waterborne finishes leave a slight hue or haze that effect the color or natural appearance on different species of wood.

 

Clarity in your finish can also be affected by flattening paste used to achieve different sheens. Keep in mind that applying a dull coating over and over can make your finish cloudy not to mention it could also give your top coat a higher sheen instead of the matt or dull sheen you were after. This is due to the amount of coating thickness being applied making the finish extremely smooth, this will kick the sheen up with a cloudy look (have you ever rubbed a spot with your finger and it got shinier? This happened because you flatten the surface to a very smooth finish.) If you are trying to have a clear no haze dull appearance you may want to try applying a gloss coating (which doesn’t have flattening paste) as the first few coats and end with your dull finish as your final coat in order to achieve clarity yet resulting in a dull topcoat.

 

Knowing that the clarity is a vital part of your finishing schedule and how it stacks up will make the difference between success and rework.

 

Till next time remember when you go to buy finish and you hear those buzz words…Do you hear are what I hear?