Paint tubes that twist and rip. They make me go Grrr. I've been struggling with one tube of Artist Spectrum Prussian Blue. The tube material isn't sturdy enough to handle twisting off an even slightly-stuck cap. This one got squeezed into an empty paint tube, and this brand will be going on my don't-buy list. I'm afraid Rembrandt might be joining it. Love the paint, hate the tube. Transferring to another tube saves the paint, but seriously, have you ever tried to get Prussian Blue out from under your fingernails?