What are Blind and Buried Vias?
As the name suggests, Buried vias are the through hole between the inner layers. The upper and lower sides are inside the board. It cannot be seen after the layer pressing，so it will not occupy the area of the outer layer
Blind vias are the vias which have not complete drill through the whole board. One side of the vias is on the surface of the board and another size is inside the board. Only one side can be seen after the layer pressing.
OSpcb could not make Blind and Buried Vias for you for the time being. So please do not send blind vias design or buried via design to us