Could I use this for signing artwork, say with acrylic ink? Or would the nozzle be too wide to give a fine line?
The Bottle Pen does not have a really fine nozzles. You can sign you work depending on the size of your piece with this product but there are other products on the market which you can use to fill with you medium and enable fine detail.
Something like the FW Mixed Media Paint Marker which are an empty pen and available with different sized nibs These can be filled with acrylic ink or other fluid medium offering greater control.
Can I use it for masking fluid, if not can I buyback fine pinned bottle without the masking fluid as already have the fluid
I know of no reason why you could not use the bottle pen for your masking fluid, you would certainly have to be careful cutting the nozzle though as you wouldn’t want too much flowing out at once. Unfortunately, we do not sell the fineliner bottle empty, however another option you could look at would be the SAA Ruling Pen (Stock code: SAARP) which is perfect for creating fine lines and grasses with masking fluid.
I hope this helps,