Okay, this is not technically a "dry material", but it'sstill a component used in ceramic chemistry, so we're going to put it in this category.
Darvan is a deflocculant and used to disperse ceramic suspensions to minimize their water content. It is a liquid alternative to the long popular sodium silicate. About twice as much is required typically (0.4-0.5%) however Darvan does offer a number of advantages. Typically soda ash is not needed as a complement and Darvan does not attack plaster molds. In addition slurries are much less sensitive to over deflocculation and are more stable. It is thus easier to reprocess scrap. However a number of engineers still prefer using a sodium silicate:soda ash mix to control thixotropic properties better, especially if little scrap is being added.
Darvan No. 7 is a high molecular weight, long chain polymer that has been used successfully as a general purpose dispersing agent for both ceramic bodies and glazes. Like 811 and 812, this poly-electrolyte shows the advantages mentioned above. Slips prepared with Darvan No. 7 show little tendency to thicken on standing (thus this version is considered better for glazes).
Chemical information per DigitalFire.com