We develop holistic principles for expressive web curation through the iterative design and study of a new medium and system, IdeaMache. Web curation is the process of gathering and assembling content into online exhibits. The linear organization of the feed - e.g., Facebook and Twitter - and board - e.g., Pinterest - constrains authors in expressing themselves. We conducted a field study of IdeaMache with 472 undergraduate student users. Quantitative, qualitative, and visual data show how students expressed themselves and developed ideas. Interaction logs show how students utilized expressive operations. We analyze students' creative works with ideation metrics of curation. Interviews expose users' underlying motivations and experiences. Visual data is compelling. While iteratively designing IdeaMache features in conjunction with the mixed methods data, we derive holistic design principles for media and systems supporting expressive web curation: direct clipping with context, diverse and heterogeneous media, freeform non-linear medium of assemblage, multi-scale organization, sketching as annotation, and novice-friendly direct manipulation command selection and parameter adjustment.
