forgive if these have been answered better already...just felt like answering the questions and thinking about this stuff myself. I went back up and read more and think that my thoughts will echo Ilaekae's quite a bit.
Originally Posted by hylandr2
You are very close to getting it. Whoever is talking to you is giving you good information. Prob is finding someone who can show how it is done and why rather than just theory, but it will make you a stronger artist if you figure it out yourself. Asking focused questions like this is always good. Do more research into looking at paintings to find these answers. Look to find these answers in the images in Art History. This is where your teachers find some of that info...finding it yourself will get rid of their "teacher filter". Same goes here.
1. Underpainting Compliment Base Color: A key to the school of painting you are studying is "contrast". Appropriate choice of value, temperature, and saturation/intensity contrasts will help the image retain vibrancy of color and reflection of natural color/tonal light vibration in the eye of the viewer. You are entering into the area called "color theory".
Paint and canvas are not as vibrant as light in life. You are studying light and how to create that feeling in the eye that "light actually has" within a painting(which does not because its mud and solvent and not the sun or a candle or a lamp). Your teachers are pointing you down the path of understanding how to "fake" the feeling of natural light in your paintings...and how to use those devices to control your communication and narrative with color composition
There are ways in which you can get colors to vibrate as light does. Having complimentary undertones is perhaps the easiest way in which you can get your light and shade to dance visually. This has to do with optical color mixing, which happens every day in front of you when your eyes are open. It has to do with the fact that light and shadow are COMPLIMENTS in all ways. Using an "opposite color underpainting technique" assists you in getting "light compliment theory" accomplished in the image. There is technique in the process of getting strokes of mud and oil to mimic what light actually does in life.
Often, light and shadow are not just to be seen as lighter or darker...but unsaturated and saturated...color compliments...warmer and cooler....LOOK FOR THESE THINGS in life if this is your path of study. You will find true subtlety of these theories and at times will even find ways to prove them wrong. That is what I love about art theory. It is a constant search to prove oneself wrong so we can learn. By having pieces of your underpainting in contrast you can begin to lure they eye around compositionally. You can create focus. You see, your teachers are simply trying to get you to control color...to see. LOOK.
2. If you paint over the entire underpainting then the compliment color underpainting technique can be used along the way so that you can make color choices. It allows the artist to be aware of colors that are brushed on the canvas as they have colors to compare against. However, there will be places where the underpainting color would be used anyway so at that point the only reason to paint over your underpainting is to gain a particular finish to the paint quality and paint surface. It does not nullify the underpainting if you are using it as a guide for accuracy or perfection of your expression. Some artists believed it to be a waste of time, others swore by it as it allowed them to do things they could not do otherwise with the paint. The underpainting is like the scaffold for which the rest of your painting sits. Some artists wouldnt use it as they believed it took from the freshness of the painting process and the loose qualities they appreciated. Most extremely polished paintings use an underpainting process. But, loose images can also do this. Rembrandts rough paintings are still using the underpainting process and they are far from stiff and clean. It all comes down to what you want to accomplish with your paint.
Your teachers are teaching a slew of painting theory from different time periods at you. What you are getting is a cross section of art theory from different time (Baroque, 19th century, Impressionist, 20th century illustration). You could study into the bones of the different periods of painting in terms of technique, color, composition, idea, feeling, mood, expression etc. This will allow you to choose which way of working best suits your needs for communication. Now that you are getting into painting 101, dig deeper.
3. Gray is a cool..or a warm... If you put any other color on it, it will seem to be a color. If you put a green gray stroke down on that gray surface and then put down a violet gray stroke the canvas base would seem like a blue gray..or a yellow gray...depending on what gray you have as your base. If it seems to be a blue in comparison and you put a warmer blue gray down then the painting base will seem like a cooler blue. Do you see where this is going?
A gray underpainting or "grisaille" was the foundation for most painting happening in the baroque time period. It was explored prior to that but became one of the primary techniques around the time of rembrandt. The easiest way to explain it is that it was used as a base for warm light paintings. There is a technique developed that requires many oil glazes and washes to be used over the gray underpainting to develop deep transparent shadows. Then, the light is painted on opaquely and this helps to reflect the light off the paint surface and back to the viewer..where the transparent glazes in the shadows draw in light and fill the shadow paint with "fill light".
Typically at that time, if the paintings were of a warm light source, the underpainting was gray. If it was a cool light source the underpainting was based in the burnt sienna range. This allows for easy and immediate seperation of temperature between light and dark as you paint...assuming you are paying attention.
Another reason to build off middle values (like gray) is that most of the things in your environment when you paint are not pure darks and pure lights. Working from middle values toward light..and toward dark...allow you to save your lightest lights and darkests darks til last more easily in an art school setting. It is simply easier for the eye to judge lights, darks and colors when there is a base down to paint on.
There many ways to use an underpainting. These are just a couple.
4. for compositional color unity...i.e. your painting looks like it is all made up of parts from the same color world and atmosphere...you can have your colors sprinkled about throughout the composition. focal areas are where you place all your best contrasts...balanced to work with your color composition. Too many contrasts might make it garish...perhaps...or perhaps not. It all depends on your image and balance of color/tonal composition and light. If your underpainting is the appropriate contrasting color for that area, then you could leave it..or paint over it with the same color if you wanted to hide the underpainting surface...if it is not the right color for that area then you would paint it out or adjust it. It is all relative. You must be the judge of that.
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