For 2016, Spectrum completely overhauled their Raku Glaze Line. Colors that had problems with going thick and crystallizing in the jar have been reformulated to eliminate those problems. 5 unpopular colors have been discontinued, but 10 exciting new colors have been added.
Unfortunately, 879 Dune is one of the glazes marked as discontinued. Once current stock is depleted, we won't be able to get it again.
The chart below shows the lineup of Spectrum Raku glazes so you can see at-a-glance which glazes are still available.