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*[http://en.wikipedia.org/wiki/16th_century 1530]
==Definitions==
*1: a black siliceous stone related to flint and formerly used to test the [[purity]] of gold and silver by the streak left on the stone when rubbed by the metal
*2: a test or criterion for determining the [[quality]] or genuineness of a [[thing]]
*3: a [[fundamental]] or quintessential part or feature : basis <a touchstone [[film]] of that decade> <now considered a touchstone of the [[city]]'s life — Michael Specter>
==Description==
A '''touchstone''' is a small tablet of dark stone such as [http://en.wikipedia.org/wiki/Fieldstone fieldstone], slate, or [http://en.wikipedia.org/wiki/Lydite lydite], used for [http://en.wikipedia.org/wiki/Metallurgical_assay assaying] precious metal alloys. It has a finely grained surface on which soft metals leave a visible trace.
The ''touchstone'' was used in [http://en.wikipedia.org/wiki/Ancient_Greece ancient Greece]. Its role in the introduction of monetary [[economy]] was explored by science historian [http://en.wikipedia.org/wiki/James_Burke_(science_historian) James Burke] in the second episode of his 1978 BBC television series ''[http://en.wikipedia.org/wiki/Connections_(TV_series) Connections]''.
It was also used by Indus Valley Civilization about 3500 BC for testing the purity of soft metals.
Drawing a line with gold on a ''touchstone'' will leave a visible trace. Because different alloys of gold have different colours (see gold) the [[unknown]] sample can be compared to samples of known [[purity]]. This [[method]] has been used since ancient times. In [[modern]] times, additional tests can be done. The trace will react differently to specific [[concentrations]] of [http://en.wikipedia.org/wiki/Nitric_acid nitric acid] or [http://en.wikipedia.org/wiki/Aqua_regia aqua regia], thereby identifying the quality of the gold. Thus, 24 carat gold is not affected but 14 carat gold will show chemical activity.
As a [[metaphor]], a ''touchstone'' refers to any [[physical]] or [[intellectual]] measure by which the [[validity]] or merit of a concept can be tested. It is similar in use to an [http://en.wikipedia.org/wiki/Acid_test_(gold) acid test], [http://en.wikipedia.org/wiki/Litmus_test_(politics) litmus test] in politics, or, from a negative perspective, a [http://en.wikipedia.org/wiki/Shibboleth shibboleth] where the criterion is considered by some to be out-of-date. The word was introduced into literary criticism by [http://en.wikipedia.org/wiki/Matthew_Arnold Matthew Arnold] in "the Study of Poetry" (1880) to denote short but distinctive passages, selected from the [[writings]] of the greatest [[poets]], which he used to determine the relative [[value]] of passages or poems which are [[compared]] to them. Arnold proposed this method of [[evaluation]] as a corrective for what he called the "fallacious" estimates of poems according to their "historic" importance in the development of literature, or else according to their "personal" [[appeal]] to an individual critic.
[[Category: The Sciences]]
[[Category: Languages and Literature]]
*[http://en.wikipedia.org/wiki/16th_century 1530]
==Definitions==
*1: a black siliceous stone related to flint and formerly used to test the [[purity]] of gold and silver by the streak left on the stone when rubbed by the metal
*2: a test or criterion for determining the [[quality]] or genuineness of a [[thing]]
*3: a [[fundamental]] or quintessential part or feature : basis <a touchstone [[film]] of that decade> <now considered a touchstone of the [[city]]'s life — Michael Specter>
==Description==
A '''touchstone''' is a small tablet of dark stone such as [http://en.wikipedia.org/wiki/Fieldstone fieldstone], slate, or [http://en.wikipedia.org/wiki/Lydite lydite], used for [http://en.wikipedia.org/wiki/Metallurgical_assay assaying] precious metal alloys. It has a finely grained surface on which soft metals leave a visible trace.
The ''touchstone'' was used in [http://en.wikipedia.org/wiki/Ancient_Greece ancient Greece]. Its role in the introduction of monetary [[economy]] was explored by science historian [http://en.wikipedia.org/wiki/James_Burke_(science_historian) James Burke] in the second episode of his 1978 BBC television series ''[http://en.wikipedia.org/wiki/Connections_(TV_series) Connections]''.
It was also used by Indus Valley Civilization about 3500 BC for testing the purity of soft metals.
Drawing a line with gold on a ''touchstone'' will leave a visible trace. Because different alloys of gold have different colours (see gold) the [[unknown]] sample can be compared to samples of known [[purity]]. This [[method]] has been used since ancient times. In [[modern]] times, additional tests can be done. The trace will react differently to specific [[concentrations]] of [http://en.wikipedia.org/wiki/Nitric_acid nitric acid] or [http://en.wikipedia.org/wiki/Aqua_regia aqua regia], thereby identifying the quality of the gold. Thus, 24 carat gold is not affected but 14 carat gold will show chemical activity.
As a [[metaphor]], a ''touchstone'' refers to any [[physical]] or [[intellectual]] measure by which the [[validity]] or merit of a concept can be tested. It is similar in use to an [http://en.wikipedia.org/wiki/Acid_test_(gold) acid test], [http://en.wikipedia.org/wiki/Litmus_test_(politics) litmus test] in politics, or, from a negative perspective, a [http://en.wikipedia.org/wiki/Shibboleth shibboleth] where the criterion is considered by some to be out-of-date. The word was introduced into literary criticism by [http://en.wikipedia.org/wiki/Matthew_Arnold Matthew Arnold] in "the Study of Poetry" (1880) to denote short but distinctive passages, selected from the [[writings]] of the greatest [[poets]], which he used to determine the relative [[value]] of passages or poems which are [[compared]] to them. Arnold proposed this method of [[evaluation]] as a corrective for what he called the "fallacious" estimates of poems according to their "historic" importance in the development of literature, or else according to their "personal" [[appeal]] to an individual critic.
[[Category: The Sciences]]
[[Category: Languages and Literature]]
