if I type:

arc({blockType: blocks.wool.black, meta: 0, radius: 8,strokeWidth: 1} );

it doenst draw an arc but if I type

arc({blockType: blocks.wool.white, meta: 0, radius: 8,strokeWidth: 1} );

it does?

I'll take a look

Hi @gingemonster ,

The arc() function is a low-level drone function. It's called by sphere, cylinder etc.
The parameter's blockType and meta should be a block id and meta information.
If you want to build black wool I recommend:

arc( { blockType: 35, /* wool */ meta: 15 /* black */, radius: 8, strokeWidth: 1} );