PAINTING IN ACRYLIC 

Acrylic is an artificial and comparatively modern type of paint (if you consider the mid-20th century modern) yet its useful qualities have made it a very popular paint type. While oil paints are still regarded as the 'premium' painting format, with higher prices, acrylics can match many of the best qualities of both oils and watercolors. 
Like watercolors, acrylics can be 'glazed' in multiple partially opaque layers if needed. But like oils, these layers do dry out after a while and once dry, won't be reactivated by water. Acrylic washes or glazes can be acheived effectively with gel mediums (matte or glossy) that when mixed into the paint, will make it more translucent and less opaque. 
 
One technique well suited to acrylics is the underpainting. You can create a subtle mix (a light gray or brown, a blue-gray, greenish-gray, ochre... all of these can work well.) and take that and layer it over the entire canvas before doing any other work. It serves two purposes - first, to ensure that every part of the canvas is coated in paint, removing those little white specks - and secondly, it achieves the aim of tinting the entire work a bit towards a particular warm or cool tone. 
 
You can also consider using sandpaper on a canvas to smooth it out a bit. This does help smooth out the surface if that is what you want. This is particularly useful when painting miniatures or miniature art. Also useful for detail work - small brush tips. 20/0 or similar seems to be an ideal size for intricate detailing. 
 
Other offbeat techniques can be used. There are many ways to apply brushstrokes, surely, but the use of palette knives and other tools extend the options available. Foam brushes can evenly apply paint and fill in a lot of cracks. Different brush sizes and shapes are useful in different cases - fan brushes are great for distant leafy vegetation, for example. It's possible also to mix powders (i.e. sand or whatever) into the paint to give a particularly rough texture. A thick volume of paint applied heavily with the brush can also be attempted, to create an impasto style. 
 
Many of the scattered methods available are rarely useful, but most are worth experimenting with in certain cases. Don't be afraid to try new things - experimentation with brushes and other materials can sometimes yield interesting insights.

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