Many people are confused between a painting knife and a palette knife. They look similar and are used in painting on canvas. So, what’s the difference between these two painting tools?
Difference in Oil Paintings: 
Palette knife painting is a type of painting that is done using a palette knife instead of a brush. This type of painting can create thick, interesting textures and patterns that are not possible with a brush. see the sample richness
Another advantage to painting with a palette knife is that artists can achieve thick texture on the canvas. By using viscous mediums that hold their shape, painters can create three dimensional looking peaks
Painting Knife
About.com defines a painting knife as “a springy, shaped, metal spatula used for painting instead of a brush.” A painting knife is a tool used to apply paint which is made of metal with a wooden handle. It has a crank or a bend on the handle, similar to the shape of a trowel, that helps keep your knuckles from touching the paint you’re applying. Even though it’s called a knife, a painting knife has blunt edges and is not used for cutting or slicing. Painting knives are available in different sizes and angular shapes: triangular, pear-shaped, rectangular, or diamond-like.
Palette Knife 
A palette knife is a blunt tool shaped like a spatula which is used in mixing paint colors, mediums, additives, etc. and scraping paint off the palette. It has a longer, straight blade with a rounded tip, unlike a painting knife which has angular shapes. A palette knife is made of metal, plastic, or wood.