In larger casting, they can be up to a millimetre (0.040 in) in diameter.To prevent gas porosity the material may be melted in a vacuum, in an environment of low-solubility gases, such as argon or carbon dioxide, or under a flux that prevents contact with the air. To minimize gas solubility the superheat temperatures can be kept low. Turbulence from pouring the liquid metal into the mould can introduce gases, so the moulds are often streamlined to minimize such turbulence. Other methods include vacuum degassing, gas flushing, or precipitation. Precipitation involves reacting the gas with another element to form a compound that will form a dross that floats to the top. For instance, oxygen can be removed from copper by adding phosphorus; aluminium or silicon can be added to steel to remove oxygen. A third source consists of reactions of the molten metal with grease or other residues in the mould. Hydrogen is produced by the reaction of the metal with humidity or residual moisture in the mould. Drying the mould can eliminate this source of hydrogen formation.Gas porosity can sometimes be difficult to distinguish from micro shrinkage because microshrinkage cavities can contain gases as well. In general, microporosities will form if the casting is not properly risered or if a material with a wide solidification range is cast. If neither of these are the case then most likely the porosity is due to gas formation. Tiny gas bubbles are called porosities, but larger gas bubbles are called blowholes or blisters.
But Threnody explains that her presence at the castle caused her father to dote on her and neglect his duties to the destruction of the kingdom; her stepmother had merely made her destructive potential literal, and forced her to confront what she was doing.The character of the evil stepmother can also be found in the genre of young adult fiction or young adult social problem novels. In Lisa Heathfields Paper Butterflies. the protagonist June suffers horrific abuse at the hands of her stepmother, a fact that she conceals from her father. Despite many examples of evil or cruel stepmothers, loving stepmothers also exist in fiction. In Kevin and Kell, Kell is portrayed as loving her stepdaughter Lindesfarne, whom her husband Kevin had adopted during his previous marriage. Likewise, Lindesfarne considers Kell her mother, and has a considerably more favorable view of her than Angelique, Kevins ex-wife and her adoptive mother, due to feeling neglected by Angelique during her childhood. The Disney film Enchanted also makes references to the "evil stepmother" belief, as the villainess is a stepmother, but her wickedness comes from her selfishness and power hungriness rather than the simple fact she is a stepmother. When a little girl tells the heroine Giselle that all stepmothers are evil, Giselle reminds her that she personally knows some wonderful women who were good stepmothers, and the fact a woman is a stepmother does not suddenly change her personality.