Fingernail hardness

A rough measure for the hardness of a plastic is its behavior when scratched with a fingernail hard plastics scratch the nail hornlike plastics have about the same hardness flexible or rubbery plastics can be scratched or dented with a fingernail. 

X-ray evidence shows the material to be completely amorphous as might be expected from such a complex mixture. The specific gravity ranges from 1.05 to 1.10. It is slightly harder than gypsum and therefore just not possible to scratch with a fingernail. Yellow in colour, it is less brittle than other hard natural resins and may therefore be carved or machined with little difficulty. The refractive index is 1.54. 

Table 14.3 contains comparative hardness values for five hardness scales including the classical Mohs scale, which ranges from the force necessary to indent talc given a value of 1 to that needed to scratch diamond given a Mohs value of 10. In the field, a number of relative tests have been developed to measure relative hardness. The easiest test for scratch hardness is to simply see how hard you have to push your fingernail into a material to indent it. A more reliable approach involves scratching the material with pencils of specified hardness (ASTM-D-3363) and noting the pencil hardness necessary to indent the material. 

In a relative sense, minerals from 2 in 33) hardness can be scratched by a fingernail 4 by a penny, and 5 to 6 by a knife blade or piece of glass This scale is strictly relative and noidincur because there is a much wider differential, lor example, hetween corundum and diamond than between... 

A simple, but not very quantitative, hardness test has been used for hundreds of years— the fingernail indentation test. The indentation that a fingernail makes in the edge of an adhesive bond or in the body of a sealant can often be used as an approximate indication of hardness of the material. 

In examining new polymers, the hardness may be estimated by using one s fingernail (Mohs 2), a brass scribe (Mohs 3), a knife blade (Mohs 4), or a piece of glass (Mohs 5). 

Also, as with Sal Palmer, there had been nothing found at the site to indicate who might have done this to her. The ground was baked too hard to yield footprints, and except for the rope fibres caught on her broken fingernails there was no trace evidence, no forensic clues left as to the killer s identity. 

The hardness of a mineral can be determined by a scratch test. The scratch test establishes how easily a mark can be made on a mineral sample using different materials. If a mark is made easily, the mineral is not very hard. If no mark can be made, then the mineral is quite hard. The hardness is then measured on a scale of 1-10, called Mohs hardness scale, named after the Austrian scientist F. Mohs, who developed this procedure. If a fingernail can scratch a particular mineral, it would have a hardness of 2.5. If a penny can scratch it, its hardness is around 3. If a mineral can be scratched by glass, its hardness is 5.5. If it can be scratched by unglazed porcelain, it has a hardness between 6 and 6.5, and if a steel file can leave a mark, it has a hardness of 6-7. Talc is the softest mineral with a hardness rating of 1, while diamond is the hardest, rated 10. 

Scratch tests are a common method used to identify mineral hardness relative to Mohs scale. Streak tests are often carried out on streak plates. Mineral hardness is a fundamental property of minerals and can be used to identify unknown minerals, hi the absence of comparative minerals, geologists often resort to common objects with a relatively well-established Mohs hardness number. In addition to glass (5.5), copper pennies measure 3.5, and the average human fingernail averages a Mohs hardness of 2.5. 

Lithium is a very soft, silvery metal. It has a melting point of 356.97°F (180.54°C) and a boiling point of about 2,435°F (1,335°C). Its density is 0.534 grams per cubic centimeter. By comparison, the density of water is 1.000 grams per cubic centimeter. Lithium s hardness on the Mohs scale is 0.6. The Mohs scale is a way of expressing the hardness of a material. It runs from 0 (for talc) to 10 (for diamond). A hardness of 0.6 means that the material can be scratched with a fingernail. 

To test the hardness of each sample, press into each sample with your fingernail and try to make a permanent mark. 

A rather unusual test is to tap the plastic firmly with a fingernail. If the sound is metallic, the plastic is likely to contain polystyrene. Hardness is another property that can be roughly tested with a fingernail applied to the underside of an object. Plastics which can be marked with a fingernail include polyethylene, polypropylene, plasticised PVC and polyurethane other types are not affected. 

A protein called keratin is insoluble in water but binds to other keratin molecules to form hard structures. Proteins like keratin are known as structural proteins or fibrous proteins. Keratin is the main component in hair and fingernails. A different protein called insulin is soluble in water and achieves a certain shape as an individual molecule. Proteins like insulin are known as globular proteins. Insulin in the bloodstream regulates glucose metabolism. 

Continue performing the scratch test with various objects of known hardness, until you find two adjacent objects on your list, such as a fingernail (2.5) and a penny (3), in between which the hardness of your sample rests. You will know you ve found this pair of objects on your list when the harder object of the pair does scratch your sample, while the softer one does not. 

Once you have found this place on the list, you can assert that the hardness of your unknown must lie between that of the two objects of known hardness on the list. For example, if a penny (3) scratches your object, and a fingernail (2.5) does not, your object must have a hardness between 2.5 and 3. 

Fingernails and toenails are composed of "hard" keratin, a very dense type of this protein. The epidermal cells of nails grow from epithelial cells lying under the white crescent at the growing end of the nail. Like hair, the nail tissue beyond the growing cells is dead. 

Mohs scale A hardness scale in which a series of ten minerals are arranged in order, each mineral listed being scratched by and therefore softer than those below it. The minerals are (1) talc (2) gypsum (3) calcite (4) fluorite (5) apatite (6) orthoclase (7) quartz (8) topaz (9) corundum (10) diamond. As a rough guide a mineral with a value up to 2.5 on this scale can be scratched by a fingernail, up to 4 can be scratched by a coin, and up to 6 by a knife. The scale was devised by Friedrich Mohs (1773-1839). 

Fingernail test n. Gouging a dried film with fingernail to form a subjective, qualitative estimate of the relative hardness and toughness. 

Using your fingernail is a satisfactory way of determing hardness. If desired a Barcol impressor, or a pencil hardness test may be employed. 

Gypsum is very soft at 2 on hardness scale of Moho (Deer et al., 1992). Gypsum is so soft that a fingernail can easily scratch it. It is characterized by a monoclinic crystal system and a perfect cleave. The specific gravity of gypsum is 2,3. It has a white streak and a vitreous luster. 

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