Every artist knows it can be tricky to get those really fine lines when painting grass or thin tree branches. Creating the density and vibrancy of the subject can be difficult. The technique I use depends on the colour (of the block-in) I'm painting over. Although one thing is essential; the block-in must be perfectly dry.
The brushes I would traditionally use to paint fine lines are the Rigger Brushes which are available here.
I have more than one technique to accomplish perfectly sharp lines in my pictures and it does depend on the colour of surface I'm painting on. For example, if I'm painting on a light surface such as tree branches over a white or light blue sky, I would thin the paint down. If I'm painting on a darker background such as painting grass I use a different technique. I want the lighter grass blades to look strong so I require thicker paint giving an impasto effect.
Assuming we have a dry, mid-tone, block-in layer already in place and we have just applied the darker shaded areas on top we can get started on adding the details.
Start with a mid-tone paint. You do not need to add any medium or thinner to it. Start to work in layers, putting mid-tones on first then building up on lighter layers later.
Flatten the brush. It helps to have more paint on the palette as you’re going to pick quite a bit of paint up on the brush. Drag the brush back through the paint then turn 90’ repeating to give you a sharp blade effect on one side and flat on the other, almost like a palette knife.
We are going to use the sharp edge to draw a thin line, using the very tip of the brush.
You can now use the brush to paint the tiniest little blades of grass. Use short strokes rather than long, as you don't want thicker, broken lines.
Maintain the shape of the brush and using small movements, touch the tip of the brush on the surface doing a touch lift, touch lift motion to create a fine line, putting the point on and lifting, connecting the small lines rather than doing one longer straight brush stroke. This also stops the shape of the brush being altered and allows us to keep that sharpness. This method can be used for short and long lines.
I would recommend resting your hand on the panel using your knuckle to keep your hand nice and steady, working from left to right across the painting. Try to keep the brush marks a consistent thickness, altering the direction of the blades of grass just slightly, so they are not all identical. The paint on the palette has an impasto effect to it, so it’s not smooth. Once dry it almost feels like sandpaper. The thicker paint has a higher concentration of pigment giving us better covering power!
If you thin the paint down using Liquin or a thinner, you won’t have anywhere near the same sort of covering power as you do with the thicker paint. You can also use the Dagger Brush in the same way, which gives a similar type of effect because it’s already in the shape of a blade. One of the benefits the Rigger Brush has over the Dagger Brush is the ability to produce a much thinner line and gives a little bit more control over the width of the blades of grass.
When the mid-tone layer is complete, continue the process with lighter hues, being careful to avoid any obvious patterns. The more random your brushwork the more realistic your painting will look.
Following these instructions will help you to use the Rigger Brush to paint realistic grass. There are of course times when you want your lines to be flat with no impasto effect. That's where you'd use a paint thinner, but for areas at the front of your scene like the grass shown in my example, having that impasto effect works really well giving sharpness and depth.
Why don't you give this a try? Just remember, for this technique, the paint consistency is all important. As a rule try not to add anything to it, unless of course it starts to dry, when a very small amount of thinner may be necessary. But always make sure the paint remains thick enough to sit well on the brush. That's the key!
You can buy my Rigger Brushes here
You can see my YouTube video on this subject below