Kamal, There are numerous possibilities that will result in Black Spots/Specs in Clear molded parts
. I would first suggest that for Clear parts, the Molding Press (Barrel, Screw and Material delivery system) be strictly dedicated to Clear resin. If your molder changes to colored resins in the same Press, you will typically see spots/specs of residual resin migrating into the resin flow from previous colored runs. This may also be a problem if your Mold is used for multiple colors since it is extremely difficult to purge and clean the inner surfaces of a mold-----and this of course is a function of the intricacy of the material delivery system ( Hot Runner Manifold, Multiple Gates, etc.). Another basic screening should be made on your raw material. Based on the grade of material you purchase, you may find that if you are getting material which contains spots/specs as typical in most standard resin grades. Optical grade resin may suite your application and has a higher quality for transparency and minimum contaminents. There are many other causes for spots/specs but I don't want to write a book here. Hope that this helps.