The early "Living Presence" LP's from the late 1950's and early 1960's had a reddish-purple label, with the words "Living Presence" in a half-circle around the top (silver print, as I recall). The Mercury "Living Presence" series and the RCA "Living Stereo" releases were, without doubt, the finest LP recordings made in the US by major labels. The Mercury "Living Presence" were produced by Wilma Cozart, and the recording engineer was named Fine (can't think of his first name right now). These LP's were recorded using a 3-mike setup, which was then mixed to 2-channel stereo. The dynamics were superb for LP's, and almost every LP in the series had wonderful clarity. The value of LP's in this series varies quite a bit. Some recordings are more highly sought after than others, and condition is very important. Most serious LP collectors are not very interested in buying LP's that are not, at least, very good, and strongly prefer near-mint condition if they are going to pay top dollar. I have bought and sold some of the "Living Presence" LP's, with prices ranging from $20-100 per LP. Many of the recordings done for the "Living Presence" series were re-released by Mercury in the 1970's and 1980's as part of their "Golden Imports" reissue program. The "Golden Imports" were not the equal of the original "Living Presence" series, but were still quite good (the vinyl was thinner, and recorded dynamics were a bit more restricted than the originals). Toward the end of the "Living Presence" issues, a few recordings were made using 35-mm tape rather than standard recording tape. Some of those recordings were quite good, although the consensus among serious listeners was that they were not equal to the best of the earlier releases. The reason for using 35-mm tape was to take advantage of the wider tape, so more recorded signal could be placed on the tape and leave more width between recorded tracks.

The other great series of LP's from this era were the RCA "Living Stereo" issues. The very first true stereo LP was issued on this series, a recording by Fritz Reiner with the Chicago Symphony Orchestra. I believe the first recording made on this series was taped in 1954, some 3 years before stereo became commercially available. The best of the "Living Stereo" releases were recorded by the recording team of Moore and Layton, who had an amazing ability to gauge the acoustic properties of the recording hall, and place mircrophones perfectly to get the best combination of direct and reflected sound. Many of their recordings conveyed a wonderful sense of ambience.

The "Living Stereo" series actually had two sub-categories:
the original "Shaded Dog" releases (RCA's trademark dog listening to the early phonograph was shaded), made from about 1957 to 1961-62, and the later "White Dog" releases (the RCA dog was white, rather than shaded) from about 1962-1964. Of the two groups, the "Shaded Dog" are by far the most sought-after and expensive. Among serious collectors, the most popular "Shaded Dog" recordings can sell for $250 or more (although $35-50 is much more typical today).

Many of the Mercury and RCA LP's from this era have been sold to collectors in Japan, who have been known to pay more than $500 for mint copies. (During the mid-1980's to the early 1990's, Japanese collectors of American jazz were willing to pay up to $1000 for mint versions of the original 1960's BlueNote recordings.)

It's interesting to compare the original LP's with the CD-reissues of RCA's "Living Stereo" series and Mercury's
"Living Presence" series. As I recall from the CD notes, Wilma Cozart assisted with some of the re-mastering of the Mercury CD reissue program. While the RCA and Mercury CD's lack the wonderful sense of acoustic space that the LP's had, they are still very good recordings by some of the finest orchestras and musicians of the era.

If you have acquired some of the Mercury "Living Presence" LP's, take good care of them because they are increasingly hard to find. I suggest giving them a good wash with a LP cleaning machine (Nitty Gritty and VPI make good ones), and then treat the LP with LAST.
You could do a search of closed auctions on eBay to get an idea. There are some books at places like Borders, etc. Yes, they did use 33mm film on some recordings. A lot of them are Eastman groups, I guess close to Kodak in Rochester.
My original Mercs that I own have purple (plum?) center labels. The value of the Mercs depends on the pressing (not just whether it's an original issue vs. a generally less desireable Golden Imports reissue, but also the stamper number, such as an fr or rfr 1), its condition (including the cover) and the particular recording. Some fetch a pretty penny in mint condition, some are not worth very much. Given the condition you say yours are in, I'd probably just enjoy listening to them, but maybe others here can refer you to some publications which could give you an idea of their value.
One last point I forgot to mention. If you are interested in getting an idea about which of the recordings in the Mercury and RCA series were the best, you might want to expore the back-issues and archives of "Stereophile" magazine and "The Absolute Sound" magazine. If memory serves, one of these mags (and I think it was "The Absolute Sound") did a long series of reviews about 8-10 years ago of the Mercury and RCA LP's. Knowing which recordings were the "best of the best" might help you determine what value your LP's have. I should caution, you, however, that LP prices have cooled off a lot in recent years. Only the most serious vinyl junkies are willing to pay $100 or more for an LP. (As an example, I have about 3000 LP's in my collection, and maybe 10% of them are titles that would sell for more than $25.)
Sdcampbell, you are pretty quick with the keyboard! Excellent post! I should point out for Honda's benefit, if he didn't know, that you can (unless they're all sold out) get a few of the Mercs and many of the RCA's as reissued by Classic Records, which lack some of the warmth of the originals but have advantages in the bass, dynamics and surfaces. On a side note, the CD remasterings have uniformly been excellent, and I agree with your description of them vs. the vinyl; wonder if Phillips could/will reissue on SACD, since they own the tapes? I find that SACD does an excellent job giving a natural rendition of recorded space, among other things; might even get more of those famous Mercury dynamics.
Also with respect to the second post by the quick-fingered Mr. Campbell, the series he's referring to is in TAS, a series of articles by Sid Marks, I believe.
thanks guys for all the friend found the mercurys on the street & gave them to me because he knows how much i love vinyl..there was even an rca shaded dog of fritz reiner & the chicago symphony gotta get him a gift now.
happy listening