The Engine House have asked artists at various stages of their career to donate print-based work, be it letterpressed, screenprinted, hand-drawn or Risographed. The pieces vary between A6 (postcard) and A2 (poster) in size and have been put into sets of six and sealed in a Mystery Tube. Each tube costs £25 and you will get work worth over £100, often with previously unseen pieces.

https://www.fredaldous.co.uk/blog/2017/04/03/mystery-tubes-islington-mill-fundraising-campaign/