It is generally accepted that the correct side of the watercolour paper to paint on is the side from which the watermark is legible. For example, if you are using Saunders Waterford paper, the correct side would be the side on which the 'Saunders Waterford' Watermark is displayed the right way round. This side will be the 'Felt Side' and should noticeably have more texture. You will notice that the reverse side will have less texture, as this side will have been in contact with the mesh of the cylinder mould.
The main difference between a Watercolour Paper Pad and a Watercolour Paper Block is that a Pad will only be gummed or bound at one edge. A Block, on the other hand, is glued along all four edges; this eliminates the need for stretching your paper if only moderate amounts of water are being used. Using a block should not be considered a substitute for stretching however, as if particularly wet washes are being used the paper will still be likely to cockle.
If you haven't stretched your watercolour paper or haven't stretched it effectively, you will notice that the paper buckles (or cockles) with the application of water. This is particularly noticeable in lighter weight papers; weights above 200lb should not need stretching.
If water is applied to un-stretched watercolour paper it will cockle. This is because the water on the paper will cause the paper fibres to expand slightly. Areas that are dry will not expand. The paper moves and buckles to counteract the expansion of the wet areas, causing unsightly wells and troughs in your finished painting. If you continue to paint on the cockled paper you will notice that the paint settles into the wells, leaving uneven washes.
The length of time you should soak your watercolour paper will depend on the weight of the paper. We would recommend that 90lb the paper should be left for 3 minutes, 140lb the paper should be left for 8 minutes and for heavy papers like 300lb, the paper should be left for 20 minutes.
The type of surface you choose to paint on will depend mostly on personal preference and the types of techniques you wish to employ in your paintings. Hot Pressed paper is an excellent choice if you are working in fine detail. Illustrators and designers also favour this surface as it gives their work a 'flat' finish that is desirable if the work is to be reproduced digitally or in print. Cold Pressed (NOT) paper has a moderate texture, which makes it a popular choice with many watercolour artists. Also a favourite for beginners, the medium surface facilitates the use of a number of techniques, allowing the artist to experiment with granulating and non-granulating colours and also working in some detail. Rough Watercolour Paper is the most textured. Its surface is full of little pits and troughs which are excellent if you really want to make the most of your granulating colours. Even non-granulating colours will settle differently on the uneven surface of rough paper, creating intricate and aesthetically pleasing patterns. Rough is also a great choice if you want to make use of bold strokes and expressive marks.