Following the recent discussion on whether the sound issues with the Dana Glilespie side of the Gem promo LP
http://www.illustrated-db-discography.nl/forum/viewtopic.php?f=7&t=1894&start=15 are the result of record wear, poor pressing or bad mastering, I thought it might be useful to provide a few tips on record selection, stylus selection and record care.
Until 1983 records the were highest quality source of music widely available. SInce then , with the advent of the CD, SACD and DVD-A that has become a moot point. (Not a discussion I'm entering into

).
So, unless one purchases brand new, never played records only, one must consider second hand, and along with that how to choose and maintain one in the best possible condition.
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Apart from good storage, obvious care or lack of, wear of a record can be determined by an interplay of the following factors:
Stylus - condition, shape and playing weight of tonearmTonearm alignmentCleanliness of the record ( before each play)Frequency of playEvery play of a record wears it out, to some extent. ( Unless you are using a ELP Laser turntable - >$US 10,000 last time I looked.). This can be minimised by ensuring the best possible combination of the above, (or buying a laser turntable)
Sixty - seventy years ago it was expected that a record would last only half a dozen plays before wear was noticeable. Luckily, by the mid 70's that changed, as the quality of average record playing equipment generally improved, though still left a lot to be desired, with high end equipment demonstrating little wear at all.
As we all know, Bowie's rarest records come from the 60's and 70s - when there was a lot of so-so equipment being used - so being able to spot wear, and identify which wear is OK becomes important.
These "average" record players often did irreversible damage to records, grinding the grooves, and especially near the centre of the record where the grooves have much more information per centimetre / inch than the outer grooves, removing a lot of the high frequency sound. Some types of sounds are affected more than others. I recall selling my mono copy of The Beatles because Sexy Sadie, with its piano, sounded dreadfully distorted, though Helter Skelter, on the same side, was OK - only the high frequencies had gone.
Cleanliness of the record ( before each play)To compound matters, most people do not/cannot remove ALL the dust from a record before playing, and some of this dust on the record gets attached to the grooves, due to the vinyl record softening/almost melting as the stylus passes by. A record with dust attached looks greyish, rather than shiny black - coloured vinyl excepted. Some of this dust may be removed with a high quality cleaning machine, or manually using various methods, though because the record has been played with dust it will have some wear.
Stylus - condition, shape and playing weight of tonearmAnother factor that potentially creates a lot of unpleasant audible wear is the stylus - shape, condition, and playing weight.
Clearly a worn stylus will wear a record immediately - depending on the wear damage, it may be like a chisel and your record will never sound as it should again.
Until the 70's the most common shape for a stylus tip was round - known as "spherical" or "conical". This shapes play silent grooves - with no wiggles, really well, but as the music gets louder and more complex, the grooves twist and turn too much for the stylus, and it either rides high, grinds the groove or both. Not good. The most common shape for a stylus tip is elliptical ( or oval) . These come in different dimensions (such as .007 x .003, or .007 x .002, etc.) These are much better than spherical stylii, as the elliptical shape is more able to navigate the groove wiggles.
When quadrophonic records were introduced circa 1974, an even better shaped stylus was developed - better because it had a higher ability to follow the groove - and "touched" the groove more - over a larger area. Both of these factors contributed to even less wear (and better sound). This shape was called Shibata. Nowadays there a number of similar shapes with different names all doing much the same job. If your turntable can work with a stylus shape like this, it's the one to go for.
BTW Spherical stylii are still made, and come with the cheaper turntables - the most common shape is elliptical.
With regards to tonearm playing weight anything over about 2 grams is too heavy- it will cause wear. Common record players of the 50's and 60's had weights of anything up to 30 grams, though many were around 10. (Lighter than the manufacturer says will also cause wear)
DJ turntables of almost all eras generally wear records more than domestic units - hence buying a played radio station copy is a "considered" purchase.
Tonearm alignmentTurntables tonearms are a bit like the front wheels on cars - unless the design is good, and the stylus is correctly aligned, the wear will increase. The most common design style, pivoted tonearms are a compromise design - they are only correctly aligned at two points - the rest of the time they are "close". For the same reason 7" records are often disproportionally worn because tonearms are almost always aligned for 10" and 12" records, whose innermost grooves are further from the centre of the turntable than a 7" record. Wear usually can be heard on the left groove first. If you have a perpendicular (or parallel arm), then you should have correct alignment on the whole record.
Frequency of playAs the stylus passes over, the groove moves - like an elastic band - and it takes up to 24 hours for it to return to original shape. If you play it again before it has returned to its original shape the grooves lose some of their shape. Play a record no more than once a day.
In summaryRecords are more likely to have worn sound closer to the centre, hence this is the area to examine the most.
Records with ingrained dust are to be avoided - ask for photos under bright lights
The louder and/or more percussive a recording is, generally the more wear is audible.
Clean records before every play including stylus before every side, and don't play more than once a day.
Ask questions about the sellers equipment, or eyeball it.
Use good equipment with a correctly aligned and weighted stylus, which is not elliptical or spherical/conical
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I've read this back and it sounds so dry..... for that I apologise.........but perhaps it may help preserve our collections for a little bit longer.