Why is my casting slip thick and gloopy?

Casting slips are thixotrophic so upon standing they can thicken. This is usually easily rectified with a thorough stirring, but if this doesn't help the slip might need 'setting up' again: Over time the deflocculant contained within a casting slip loses its electrical charge resulting in loss of efficacy. This process is accelerated by changes in temperature, and stoneware slips with a higher clay content are most affected. This is an industry acknowledged issue affecting all casting slips regardless of manufacturer but it can be easily remedied by further deflocculant addition. Add 1-2 drops of Sodium Dispex and stir well. Repeat until desired fluidity is achieved.