Hey Kai! So here the word shade refers to the size of the cauldrons. Generally the word shade is used in context with color, shade is how we “measure” colors, we have different shades, or tones, or hues. Each color shade makes the color either darker or lighter, so it changes the brightness, contrast, etc of the color. But here is being used as a unit of measurement. So it would be a little difficult to say thay the cauldron was 2 cm to thin, or 4 inches too thick. Although possible those measurements are hard to make at plain sight let alone on an item like a cauldron. So by saying is just a shade too thin we say that is just a little bit too thin or that is just about the right size. Let me know if you need further explanation!