I need to create a highly detailed painting at a large format somewhere between 3.75 x 3.75 ft and 5 x 5 ft that can then be scanned and printed at twice the size, while maintaining the utmost crispness/clarity in the finest lines. The client originally loved a pen/ink/watercolor piece I did, but I think increasing the size of pen/ink would show that ink edges on watercolor paper can be a bit soft/frayed, so preferably watercolor or a watercolor gouache combination. I need a paper or board that has the following criteria:

-ultimate smoothness (so that lines are clean and paper grain is less noticeable with enlargement)
-can handle a massive wash (to depict an underwater scene)....including minimized warping and maximized smoothness.
-is strong and can handle being worked a bit--so less pilling/pulling/fraying of paper
-comes in a large size.
-any other criteria you think could be helpful

I can potentially go down in size a touch if there is an ideal paper that doesn't come that large.

We carry two professional watercolor papers that fit your criteria. We recommend Saunders Waterford Hot Press or Lanaquarelle Hot Press.

Saunders Waterford Hot Press is the smoothest hot press paper in the market which allows for crisp/detailed lines. This is a 100% cotton mould made paper sized for watercolor and the sheets come with four deckled edges. The oversize sheet size of 40"x60" comes in a hefty weight of 640gsm which allows for heavy washes without the fear of warping. For larger work, Saunders Waterford is offered in a roll size of 60"x10yd in 425gsm.

Lanaquarelle Hot Press is another high performing 100% cotton mould made watercolor paper. The oversize sheets are offered in a size of 40"x60" with four deckled edges and a weight of 640gsm. We also offer rolls size 51"x11yd in 640gsm which allows you to work large without compromising paper weight.

Both papers offer a smooth surface for crisp line work as well as reduced pulling, sized internally and externally which prevents warping when washing and comes in sizes that meet your desired size of 3.75 x 3.75ft and 5 x 5ft.