Baroque and Renaissance, you need to aim for pure chords and again Jack has a point about the nature of our traditional music, not Just Scottish but English and Irish as well. Many of the tunes are pretty old and modern ones are essentially being written an an old style.
sorry,this is not correct,nearly all the traditional English irish scottish repetoire,has been written since the time of equal temperament.,Please correct,me with detailed lists of tunes and times,if you believe I am incorrect.
J S BACH favoured and expoloited ET.J S Bach[ 1685 TO 1750].but there were others long before him
the majority of the repertoire was not written before ET.
O Carolan for example was 1670 TO 1738.,was a contemporary of Bachs
here is wikepedia on ET.

was one of the first advocates of twelve-tone equal temperament in a 1581 treatise, along two sets of dance suites on each of the 12 notes of the chromatic scale, and 24 ricercars in all the "major/minor keys". His countryman and fellow lutenist Giacomo Gorzanis had written music based on this temperament by 1567. Gorzanis was not the only lutenist to explore all modes or keys: Francesco Spinacino wrote a "Recercare de tutti li Toni" as early as 1507. In the 17th century lutenist-composer John Wilson wrote a set of 26 preludes including 24 in all the major/minor keys.

Historically, there was a seven-equal temperament or hepta-equal temperament practice in ancient Chinese tradition.[1][2] The first person known to have attempted a numerical specification for 12-TET is probably Zhu Zaiyu (朱載堉) a prince of the Ming court, who published a theory of the temperament in 1584. It is possible that this idea was spread to Europe by way of trade, which intensified just at the moment when Zhu Zaiyu published his calculations. Within fifty-two years of Zhu's publication, the same ideas had been published by Marin Mersenne and Simon Stevin.

From 1450 to about 1800 plucked instrument players (lutenists and guitarists) generally favored equal temperament. Wind and keyboard musicians expected much less mistuning (than that of equal temperament) in the most common keys, such as C major. They used approximations that emphasized the tuning of thirds or fifths in these keys, such as meantone temperament. Among the 17th century keyboard composers Girolamo Frescobaldi advocated equal temperament. Some theorists, such as Giuseppe Tartini, were opposed to the adoption of equal temperament; they felt that degrading the purity of each chord degraded the aesthetic appeal of music, although Andreas Werckmeister emphatically advocated equal temperament in his 1707 treatise published posthumously.

String ensembles and vocal groups, who have no mechanical tuning limitations, often use a tuning much closer to just intonation, as it is naturally more consonant. Other instruments, such as some wind, keyboard, and fretted instruments, often only approximate equal temperament, where technical limitations prevent exact tunings. Other wind instruments, that can easily and spontaneously bend their tone, most notably double-reeds, use tuning similar to string ensembles and vocal groups.

J. S. Bach wrote The Well-Tempered Clavier to demonstrate the musical possibilities of well temperament, where in some keys the consonances are even more degraded than in equal temperament. It is reasonable to believe that when composers and theoreticians of earlier times wrote of the moods and "colors" of the keys, they each described the subtly different dissonances made available within a particular tuning method. However, it is difficult to determine with any exactness the actual tunings used in different places at different times by any composer. (Correspondingly, there is a great deal of variety in the particular opinions of composers about the moods and colors of particular keys.)

Twelve tone equal temperament took hold for a variety of reasons. It conveniently fit the existing keyboard design, and was a better approximation to just intonation than the nearby alternative equal temperaments. It permitted total harmonic freedom at the expense of just a little purity in every interval. This allowed greater expression through enharmonic modulation, which became extremely important in the 18th century in music of such composers as Francesco Geminiani, Wilhelm Friedemann Bach, Carl Philipp Emmanuel Bach and Johann Gottfried Müthel.

The progress of Equal Temperament from mid-18th c. on is described with detail in quite a few modern scholarly publications: it was already the temperament of choice during the Classical era (2nd half of the 18th century), and it became standard during the Early Romantic era (1st decades of the 19th century), except for organs that switched to it more gradually, completing only in the 2nd decade of the 19th century. A precise equal temperament is possible using the 17th-c. Sabbatini method of splitting the octave first into three tempered major fifths. This was also proposed by several writers during the Classical era. Tuning with several checks, thus attaining virtually modern accuracy, was already done in the 1st decades of the 19th century. Using beat rates, first proposed in 1749, became common after their diffusion by Helmholtz and Ellis in the 2nd half of the 19th century. The ultimate precision was available with 2-decimal tables published by White in 1917