Getting blend modes like Multiply and Overlay right
Paint by Zaweba has 46 blend modes in the Layers panel, from Multiply and Overlay to Pass Through, and previews each one on the canvas as you hover.
A blend mode that looks wrong is almost always fixed in the Layers panel. Select the layer, open its blend mode list and choose again. Paint by Zaweba has 46 modes and previews each one on the canvas while you hover over it in the list, without adding an undo step, so you can try Multiply, Overlay and their neighbours in seconds and keep the one that looks right.
Blend modes decide how a layer's pixels combine with the layers below. Multiply darkens, Screen lightens, Overlay adds contrast. When the result seems off, the cause is usually one of a handful of simple things, and none of them needs a redraw.
Check the obvious first
Make sure the right layer is selected. A mode belongs to one layer, and it's easy to set it on the layer you meant to leave alone. Then check opacity and fill. A layer at low opacity will make any mode look weak.
Next, look at what sits below. Multiply over white does nothing, because white multiplied by anything leaves it unchanged. Overlay over flat mid grey does nothing either. If a mode seems to have no effect, the layers underneath are often the reason, not the mode itself.
Groups and Pass Through
Groups have a mode of their own. Pass Through, a mode only groups have, lets each layer inside blend with everything below the group. Give a group an ordinary mode instead and its layers are combined with each other first, and then that result is blended on top as one picture. If a Multiply layer stopped working when you put it in a group, the group's mode is the place to look.
Knowing which mode to reach for
Multiply is for shadows, line art over colour and anything that should only darken. Screen is its opposite, for glows and light. Overlay and Soft Light add contrast and are good for texture and dodge and burn layers. Colour and Luminosity separate colour from brightness, useful for recolouring or for sharpening without colour shifts.
Paint by Zaweba also has the less common ones: Dissolve, Linear Burn, Darker and Lighter Colour, Vivid, Linear and Pin Light, Hard Mix, Subtract, Divide, Grain Extract and Grain Merge, Negation, Reflect, Glow, and LCh and HSI modes. If you are matching a file made in GIMP, the Grain modes and the LCh modes will feel familiar.
Modes for painting tools
Two modes, Behind and Clear, belong to the painting tools and fills rather than layers. Behind paints only where the layer is transparent, so you can add colour under existing line work without touching it. Clear removes pixels as you paint, like an eraser driven by the brush engine.
Using the hover preview well
The preview is the quickest way to learn modes. Put a texture or a colour layer over a photo, open the list and run the pointer slowly down it. You'll see each result on the actual picture. Because hovering adds nothing to the undo history, you can explore freely and only click when one looks right.
Getting a good result
When you settle on a mode, adjust the layer's opacity next. Most modes look best somewhere below full strength. If you need a mode to affect only part of the picture, add a mask to the layer rather than erasing, so you can change your mind. And if a layered file came from another program, check each layer's mode once after opening, since that is where editors most often disagree.
Getting blend modes right is mostly about knowing where to look. In Paint by Zaweba every mode stays editable, so nothing you try is permanent.
