Rare Northwood dome covered butter.  This pattern was named Optica by Bill Heacock.  The scarcity of this pattern is evidenced by the omission in the classic Northwood books as well as the Heacock series. It is an absolutely beautiful pattern which comes in two known decors. The positive attribution by Heacock was made based not only upon color but finials of the items. There are two or three pattern issued by Northwood mentioned in ads that have not yet been identified.  It is believed that this is one of them. This piece is electric blue, with inside optic panels, seen in the photo, which significantly adds to the pattern. There is a small chip on one of the base scallops and a chip on the butter base rim, not seen with the cover on (see close up photo).