Why is the SSV EOK not one full piece of quartz

The SSV requires a very specific ID of glass for the heater cover and this is only possible with boro.  Having the 10mm joint also allows the same dish to be used on the SSV and the SUP

What causes color striking glass to change color

Many times it is the silver that is added, or crystals in the glass need to form.  Annealing will help the crystals to grow and give the desired color.  Ruby by Northstar is an example of a striking red, while double amber purple is a striking color mostly done in the flame.