Typical flow control agents are for example, polyalkyl acrylates and methacrylates, fluorinated polymers such as fluorinated esters of polyethylene glycol or propylene glycol, ethyl cellulose, silicones such as dimethyl polysiloxane or methyl phenyl polysiloxanes, polyvinylpyrrolidone having a weight average molecular weight of about 3,000 to 500,000 or mixtures of polyvinylpyrrolidone and silica.