The Practical Painter: Class Notes

Turpentine - traditional, but very smelly & toxic. Frequently causes headaches.
Turpenoid - lower odor, still toxic but slower-acting. Can still cause headache.
Odorless Mineral Spirits (OMS)- similar odor level & toxicity to turpenoid. Reportedly better for use in mediums.

No matter which type you use, always have good ventilation. Long-term exposure is bad.
Most schools (including this class) don't allow turpentine, only turpenoid or OMS.
It's possible to paint without using solvents at all. Walnut or linseed oil can be used for cleanup, and to thin paint.

Lead whites (Cremnitz, Flake, & Silver White), cadmium paints, and cobalts are especially toxic.
For some of the newer colors such as Quinacridones and Perylenes there isn't a lot of data about the long-term health hazards. Err on the side of caution.
The most direct route for poisonous pigments is through cuts in the skin. Be wary of things like hangnails or dry/cracked skin that may not register in your head as a cut.
Also be aware of eating and drinking while or after handling paints. Always wash your hands before eating and drinking. Be careful with your coffee cups and water bottles.
Gloves are generally effective as long as care is taken putting them on and taking them off.
Theoretically, unbroken skin is an effective barrier to harmful pigments. However, there are some studies that suggest that solvents such as OMS, Turpenoid, or turpentine break down the skin's oily barrier and allow the pigments to enter.
You have to decide your personal level of safety and comfort.

Wipe out the initial drawing slightly- so the lines are still visible but almost gone.
Take a slightly darker color and make corrections
Repeat as necessary

If it moves when your eye position moves, it's a reflection. Don't be deceived.

JC Leyendecker - shapes modeling factors are usually very clearly delineated, or clearly delineated to begin with and then made more subtle later
Igor Grabar - modeling factors are clearly laid in, but their exact shape is left undecided. As the painting progresses, the shapes are honed where necessary.

Determine the shapes that will most clearly indicate the shape of the form to the viewer- whether or not they are actually visible. Then, amid the chaos of all the various details we do see, pick out the ones that line up with those shapes.

Dividing line between light and shadow.
If you haven't clearly indicated at least the terminator, the viewer will be lost. Find the terminator of every form.
Follow the terminator from the top of the form, all the way to the bottom. Follow it all the way until it ends. Even better- follow it all the way around the form- even the parts you can't see- so you understand what's happening with it in three dimensions.
The shape of the other modeling factors is heavily influenced by the shape of the terminator.

There might be a form that is tilted in such a way that it never reaches the light modeling factor. Still, look for a progression of values that indicates that the form is turning- it will still get darker as it approaches the terminator, though it might be subtle. This is usually better than just leaving it one flat value outside of the shadow, since the form may appear to be more cube-like rather than rounded.. The part where it gets darker could be called its "local halftone".

The values of the modeling factors should be arranged in such a way that the form appears to have a local color comparable to what it has in life. In general, this means making each modeling factor lighter for a form with a light local color than the corresponding modeling factors on a form with a darker local. So, the halftone on a lighter object should be lighter than the halftone on a darker halftone. The same goes for shadow & light.
If the local is not held, the modeling factors will appear to be stripes on the form rather than indicating the shape of the form.

The Practical Painter