Vases We recommend hand washing Iittala vases. If there are stubborn stains on your flower vase, soak the vase in1dl laundry detergent to one liter of water. Do not scrub, as scouring powder or abrasive scrubbing pads scratch and spoil the surface. The so-called burning lens phenomenon may damage objects and surfaces in the vicinity of the glass object. To avoid this, do not leave a lens-shaped thick glass object or vase filled with water in direct sunlight.