A chatroom comment goes
"Tamasa puranas mean most of content are tamasa. But they also contain sattvic and rajasic contents though at a lower proportion. Similarly, Sattvic puranas are mostly Sattvic, but contain rajasic and tamasic content albeit in lesser proportions. It is combination of three sattvic, rajasic and tamasic content. But in Sattvic puranas , sattvic content is much more than rajasic and tamasic content."
Without defining Tamasic, Rajasic and Satvic content independent of Puranas - this is circular reasoning.
Are there a priori definitions of Tamasic, Rajasic and Satvic content in scripture?