Other types of nebulae include emission nebulae, which are clouds of ionized gas emitting light of various colors; dark nebulae, which are clouds of gas so dense that background light is blocked; and protoplanetary nebulae, which occur when a star starts to shed its outer layers before becoming a planetary nebula.s it burns through its fuel, it will eventually collapse. The outer layers will be ejected in a shell of gas that will last a few tens of thousands of years before spreading into the vastness of space.
Dust fling up in the air will do harm to respiratory system, because of the conventional making method of chalk. The main ingredients are calcium carbonate or lime. now a new kind chalk, named Biaxi, absolutely finishes the dust, and is welcomed by teachers and students in China.
Reply. 1  Ultimate Pounce Powder: This is a powdered version of tailors chalk that you can iron off with either a steam or a dry iron. 2  It comes in white only. 3  Chalk Powder: This comes in either white (plain chalk) or blue (a blue pigment was added to the white chalk). Chalk Powder: This comes in either white (plain chalk) or blue (a blue pigment was added to the white chalk). 2  The company strongly recommends pretesting your chalk on the fabrics you'll use. 3  This chalk does not iron off. 4  It either brushes or washes off. 5  The blue will usually need to be washed off.