What is the purpose of an underpainting?

Question

As I got interested in painting in oil and acrylics (and other covering techniques), I came across the term 'underpainting', i.e. a painting under the actual painting, that sometimes exhibits color, and sometimes only the tonality of the image to be.

It seems that the underpainting is almost always completely covered once the painting is finished. So what is the purpose of an underpainting when you could also directly paint on the real image (supposing that I sketched out my design with graphite or charcoal)?

Answer 1

I use under painting for a variety of reasons.

Conventionally, it is useful for extremely faint variations in color, implied-texture or reflectivity. In this respect, it is similar to adding a wash over a portion of the dominant color, as it subtly affects the final appearance without adding distinct brush strokes or delineations. I find under painting to be slightly easier to control than washes because the pigments which I use for under painting are less dilute and therefore quicker drying than their wash equivalents.

A less conventional usage is to mark the center point of a zone or to layout a grid upon an area which will ultimately be invisible in the final product, but is useful for determining proportions prior to the addition of the outer obscuring layers. For example, when laying down shadows which are being cast by multiple identical objects and at nearly identical angles to the light source, it is helpful to have an almost invisible grid (like graph paper) present. It helps me be more consistent and to adjust the angles with uniform variation between each of a series of shadow-casting objects.

My final use for under painting is for low risk experimentation. Laying out a rust pattern or a dirty spot on an otherwise pristine rendered subject is daunting. You've finally got the thing looking exactly like you want and now you just need to scuff it up a bit to make it look more real. But a little too much or even a little in the wrong spot will ruin your hard won rendering. These are the moments that make brush hands quiver.

Which is why I design my rust and scuffing before hand, to get it right before I add all the pretty paint and shine. Then, if I have to go back and strengthen the abused area after it has become too pretty, I have the still barely visible tone of the under painting ( or at least my memory of it ) to guide my hand.

Answer 2

The reasons I like to use underpainting when doing art in oil or acrylic are:

• Sometimes having small/subtle areas where the underpainting shows through can add interest to the painting. Some of the underpainting my not be so subtle, it can be vivid or even bright.
• More layers of paint help the finished look. It can make your painting look cheap if it seems you are being skimpy with your paint.
• It is a good way to build texture.
• Cheaper, unappealing, or leftover mixed colors can be used up first, which means saving money and is more environmentally conscious than throwing it away.
• Depending upon your support (canvas, wood, etc.) and its finish, meaning how porous it is, can determine how much paint will be sucked up. If you don't or can't add a layer of gesso, the underpainting can help seal the surface.
• Once a painting is blocked in with an underpainting, details are easier to imagine and build on. This is especially true when it comes to the composition, shadows, and proportion.
• You should regularly step away from your art to take a break and see it from a good viewing distance, which depends on the size, but at least 10 ft or more and the underpainting is easier to see, then the first step of a simple outline drawing.
• It's good to practice, helps to figure out which brushes are working for that particular painting, and is way easier to make changes to both.

Answer 3

Two main stages of underpainting

Underpainting (or toning) eliminates the harsh, intimidating white canvas and allows you to paint freely without worry about ‘filling in’ the white. Use a big brush to paint a wash of burnt sienna.

That's a quote from Seven Steps to a Successful Painting on the Thought Company website. Each step is illustrated and, I think, offers a foolproof approach. Underpainting is a crucial early task. Why?

It helps you identify the major values (darks and lights.) By identifying these, it forces you really look at your subject, and see if the composition will work.
As a beginner I had no idea how important values were until attending some well-run art classes. Wish I had known earlier!

I have included a sample of a still life and value study from underpainting, at yesterday's oil class. The next stage is to add colour. I have probably made mine too detailed, but that's okay. I got excited.

Mitchell Albala's website has an excellent discussion covering several ways to do underpainting (illustrated): What Color is Your Underpainting? The Monochromatic and Two-Color Methods

Answer 4

The underpainting is for glazing. You put transparent pure color very thinly over your underpainting, dry, glaze, dry, glaze. These thin washes add volume without eliminating or covering up the underpainting. If you use white paint with any colors, it's no longer translucent.