Because it is so readily attainable, flour glue is the stalwart water soluble glue used by mosaicists.  It is used in paper faced, reverse indirect method of making mosaics.  It is not as strong as rabbit skin or bone glue but for smaller mosaics it can be very convenient.  We include a recipe for flour glue in the Knowledge section of our website.  However, if you want a glue ready-to-go, this is pre-mixed and imported from Italy. 

More information on the Ravenna method can be found in our Knowledge base, under Methods.