Sometimes referred to as interlaggio, the application of a fabric, preferably linen, to a surface to be watergilded during the initial sizing (glue/sealing) stage can help prevent the subsequent gesso from developing crack mechanisms. I've usually rummaged through piles of fabric until I've found something fine and with a fairly open weave but I've decided recently to actually choose a fabric specifically for this purpose and standardize this part of my operation for gessoing and gilding large surfaces where gesso cracking is more likely.
I never knew there were so many forms of linen, some of it quite costly. But I did find something from a distributor called Rag Finders but when I returned to the fabric store today to buy more there wasn't any left in stock. I also learned that different types of linens are purchased frequently so it may be difficult to buy the same exact linen every time. So, I guess if you find something you really like, buy a lot.
I have found that when water gilding large flat surfaces, the gesso can have a tendency to develop hairline cracks. Fabric has been used for centuries for reinforcement of gesso and plaster surfaces and can help minimize or prevent these cracks from occurring. During the first step of water gilding - applying hot size (glue) to the wood surface - I like to size the front (and back if applicable) and let it dry and then apply another coat of glue to adhere the fabric. Saturate the wood surface with size, lay the linen on top and apply additional size to the top of the fabric, virtually saturating it. Make sure the linen lies flat across the wood while smoothing out the wrinkles with your fingers. Some people prefer to actually soak the fabric in the glue itself before applying it to the wood. After the glue dries after 24 hours, trim any loose ends of the fabric and gesso as normal.
Historically, the use of fabric between the sized surface and the gesso has also been used on metal before gilding. There is some evidence of this from early Egyptian gilding although it's a method most suitable to porous wood. The fabric will help the gesso to adhere to a non-porous surface but it will likely not be as long lasting as when done on wood.