To avoid panting with black is a common truism for traditional painters that will save your saturation in the lower values of your painting. When painting a naturalistic scene in a traditional medium, you are in a loosing war against the cost of saturation. (saturated pigments tend to be more expensive.) Ivory black and lamp black are very cheap pigments, hence the mixture of black paints tends to have more pigment vs medium. Also, Pigments lose saturation over time. so vibrant paintings you made 10 years ago can start to become grey.
The area of your painting where the temperature loss will become more daunting is the shadows. They tend to be a cool temperature and have a lower value and saturation. This is one of the reasons why it’s dangerous , especially for a student to use black; And this is the reason why a lot of traditional painters plot their shadows with washes of earth pigments: Burnt sienna, burn umber etc.
The other reason is convenience: Leaving you some space at the bottom and top of the value structure for final touches. Once you reach the floor value of pure black it’s hard to go back up, especially if the rest of the values are down with that black. Same for white. If the key of your painting is too high, it’s hard to add any detail without just burning the rest of your picture. So keeping some floor and headspace for the final details can save you a lot of headaches! And this is especially true for black paints since they tend to have so much pigment in their mixtures
In digital media it can also be beneficial to avoid blacks, or at least clip-mask them into a black with a little temperature in them at a early stage of coloring. I can’t really explain the reason for this exactly, but neutrals and especially black and white have a lot of visual pull in a monitor that displays thousands or millions of colors. Just adding a hint of temperature to your blacks and whites can make them gentler on the eye and keep the colors from becoming muddy*.
(*Muddy colors are a result from disorganized value and temperature structure between your lights and shadows.)
So your teacher was right, he was just either too lazy of busy to explain all that shit!
To avoid panting with black is a common truism for traditional painters that will save your saturation in the lower values of your painting. When painting a naturalistic scene in a traditional medium, you are in a loosing war against the cost of saturation. (saturated pigments tend to be more expensive.) Ivory black and lamp black are very cheap pigments, hence the mixture of black paints tends to have more pigment vs medium. Also, Pigments lose saturation over time. so vibrant paintings you made 10 years ago can start to become grey.
The area of your painting where the temperature loss will become more daunting is the shadows. They tend to be a cool temperature and have a lower value and saturation. This is one of the reasons why it’s dangerous , especially for a student to use black; And this is the reason why a lot of traditional painters plot their shadows with washes of earth pigments: Burnt sienna, burn umber etc.
The other reason is convenience: Leaving you some space at the bottom and top of the value structure for final touches. Once you reach the floor value of pure black it’s hard to go back up, especially if the rest of the values are down with that black. Same for white. If the key of your painting is too high, it’s hard to add any detail without just burning the rest of your picture. So keeping some floor and headspace for the final details can save you a lot of headaches! And this is especially true for black paints since they tend to have so much pigment in their mixtures
In digital media it can also be beneficial to avoid blacks, or at least clip-mask them into a black with a little temperature in them at a early stage of coloring. I can’t really explain the reason for this exactly, but neutrals and especially black and white have a lot of visual pull in a monitor that displays thousands or millions of colors. Just adding a hint of temperature to your blacks and whites can make them gentler on the eye and keep the colors from becoming muddy*.
(*Muddy colors are a result from disorganized value and temperature structure between your lights and shadows.)
So your teacher was right, he was just either too lazy of busy to explain all that shit!