Some pigments may be toxic, like lead pigments used in lead paint. These pigments have slowly been replaced with the minor toxic materials, like titanium dioxide. The titanium dioxide is normally coated with aluminum or silicon oxides to achieve improved external durability, and enhanced hiding characteristics. These improvements are possible due to the spacing inside the paint film. Pigments are categorized as either synthetic or natural. Synthetics include blanc fix, synthetic silicas, and precipitated calcium carbonate, while the natural pigments include various clays and silicas. Fillers are a particular category of pigment that is used to compact the paint film, integrate the structure, and augment the paint volume. Fillers normally consist of the inert materials, like lime, clay, etc. Floor paints subjected to scratch may also include delicate quartz sand to serve as filler. However, all paints do not include fillers, though some paints include large quantities of pigment, fillers, and binders.