Thanks Neil - that makes sense.
I do not remember the particular record I used for that photograph with the UV light. I may try to research that from the small amount of label print that shows. That could give a clue about when the record was made. There were times in the '80's when records were made more cheaply and re-used vinyl was one way that happened. The base material used for vinyl formulations can vary with varying quality control from manufacturers. There are only a handful of vinyl pellet suppliers and they have a dozen different formulas they use, including varying pigmentations. If the lower quality vinyl is re-used, what do you think happens? We can't clean the noise out of noisey vinyl. "Virgin vinyl" is somewhat a 21st C. phenomenon in reaction to a marketplace recognition that quality records are in demand. Michael Hobson of Classic Records was something of a pioneer toward better quality.
Tim,
Recall the book para "IV.4.b The staining in Figure 9 may be caused by using recycled (repressed) records whose label(s) were not completely removed per a conversation at VPI™ Forum, General Audio, “UV Inspection of Records Results” thread of Tue Mar 10, 2020 2:12 pm (56). A person who worked at Columbia Records factory in 1972 and 1973 was in the department that supplied the record material to the presses. The person indicated that the equipment that removed the labels from returned or over-pressed records would frequently malfunction. Labels were then part of the recycled vinyl mixed with virgin material used for pressing records that were allowed to be pressed with recycled material."
I have records dated the 1980's that identify as being pressed with "virgin vinyl" so that concept does not appear to be anything new. Otherwise, even today, there is re-pressed vinyl to be used; it's the vinyl trimmed from the pressing.
"If the lower quality vinyl is re-used, what do you think happens?". The record physical properties will be different. Once the material has been subjected to heat during the first pressing, some of the additives are expended, so when reheated, it's not the same. Based on what RCA said years ago - "IX.1...“It is a somewhat softer formulation than we had initially expected but with well-defined and controllable elastomeric properties.”, and the analysis that RCA Dr. Max did showing that the vinyl deforms/moves under stylus pressure, and what I hear (mid-high frequency emphasis), it all points to that repressed material is a harder/stiffer compound.
So, if the compound is stiffer, the stylus tracks the modulations differently, and it may be more pronounced with a Shibata type stylus versus an elliptical. It's well known and mathematically shown that the elliptical stylus radius prevents it from accurately tracing the maximum modulations (velocity) than can exist at the higher frequencies and this is illustrated in the book Figure 39 and described paragraph XI.4.5.b. However, the softer virgin vinyl compound will naturally tend to ever so slightly attenuate the peak modulations - the vinyl is ever so slightly bending/deforming proportional to the stylus pressure. So, the Shibata with greater contact area yields lower contract pressure (VTF/contact area) will cause less deformation - ergo it tracks the groove modulations more accurately with greater '"detail". The elliptical with lower contact area yield higher stylus pressure causing more deformation - ergo it tracks the groove modulations with less detail; often with a characteristic "softer" sound. Repressed material if stiffer (and that is my contention) shifts everything upward - more mid-high frequency emphasis which is consistent with what I hear and worse with a Shibata type stylus than an elliptical.
Take care,
Neil
