Modifying default font properties for piece titles

If you have multiple pieces (e.g., Kyrie, Gloria, Credo, etc. in masses) in a large work, you can use multiple \score parts and use the piece header field to supply a title for each of the pieces. However, the font is very small. You can either directly put the markup into the piece=... header field, or better re-define the scoreTitleMarkup function in the \paper section.