To expand on @BillKerr comment, "Lock brush to view" scales the brush with the zoom: the ratio
brush size/window area remains constant, so that at high zoom factors you don't get a brush that is bigger than your image window. In effect this shrinks the brush as you zoom in. If course if you start with a 3px brush, at 3800% zoom it is 3/38=0.1 pixel and is inoperative.
Further more, the
1. Pixel brush is "parametric". Gimp has two kinds of brushes:
- "parametric" brushes (
.vbr files), that are simple shapes defined by a few parameters: shape (circle/square/diamond), radius, and sides. These are the ones that you can edit with the brush editor. Under the hood they are close to vector graphics.
- "bitmap" brushes, that are plain bitmap images (the
z. Pepper brush, for instance)(
So, when you look closely, the
1. Pixel brush will always be at least 3px (one pixel for center, and 2x1 pixels due to radius=1. If you want a real 1-pixel brush, it has to be a bitmap brush. Gimp comes with such a brush, called
Pixel (1x1 square).