Blending can be done with many different tools with many different techniques.
Foundation for example can be applied with the fingers, a variety of brushes, sponges or directly pumped on to the face and then a blending tool is used to even it out and 'blend' the product into the skin.
Sponges used slightly damp or dry are used to set the product into the skin and smaller sizes would be used to set into smaller spaces, such as concealer under the eyes.
The sponge would be used in a rolling motion in order to set the product instead of just swiping it around, to avoid streaking.
A stipple brush can be used to apply the foundation over the face and again, smaller ones for concealer, but be careful not to 'streak' the product with the brush. Use it in small dabbing motions instead.
A large flat 'concealer' brush can also be used to apply foundation all over the face and then once applied, a sponge is used to set it, again using a rolling motion.
There are also a variety of oval concealer brushes that people like to use to apply and set.
Some people prefer just their fingers, but in my experience thats not a bad idea for just the concealer as the warmth of your body helps warm the product and can set it a little easier, but not for all over the face.
Whatever you use, if you 'roll' instead of 'swipe', you will set the product a lot better.
I also don't believe you need a setting powder over the entire face, just under the eyes and in areas that are oily. Again, no rules here.
The idea behind blending and 'rolling' is to set the foundation and concealer evenly into the skin so it makes the face look flawless without streaks. And don't forget to blend downward toward the neck area to avoid the 'face mask' look.
Rolling avoids streaking and makes the pores look more evenly covered.
Remember, practice makes perfect.
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