Does LAST Preservative DULL sound?

Nice response, Elizabeth. FWIW, from my experience, the stuff works, I recommend it.

I can say that it does not appear to have any long-term adverse effects. I've been using it since it was introduced. No records show any signs of wear, the stuff is not sticky so it won't cause problems with holding dust, etc.

I do clean all records, particularly brand new records, very thoroughly before applying the last. I also buff the record quite a bit more than recommended, because the product does leave a few visual markers (dull blotches on the run-out area) if the record is not thoroughly buffed.

After application, the record feels smoother and there is obviously less friction when a brush is passed over the record. Static buildup is also significantly reduced.

The big negative is cost. I buy it in the big bottle ($160), which makes it significantly cheaper on a per once basis, but it still is quite expensive.

I will not comment on the effects of the LAST products because I do not use them. I would like to say that the argument that the LAST treatment reduces the "openness" of the sound of vinyl and "smooths over detail" have been around for many years. I also know people who swear by LAST and treat all their vinyl.
Some "tweaks" have no effect, some have obvious effects but no always positive. Then there are the ones that seem to make subtle differences and there is a divide in opinion on the merits of the changes. This seems to be one of the latter.
The opinion that this may be the typical reaction of the "tweak police" may be valid. It may be the case that LAST has beneficial effects of protecting vinyl at the expense of a slight reduction in high frequency information. I dont know. Whatever your opinion is on the product, remember this debate is not new, and as they say "dont kill the messenger".

While I no longer use it (for various reasons, mostly due to cost and convenience, and the fact that I now have a RCM), all of the records I treated with in almost 20 years ago sound great.
(In fact, becasue of this, I have seriously been thinking of starting to use it again.)

My two cents worth.

I still use it on lp's that I expect to play a lot, say 8 or 10 times a year. But I'm very careful with it, and only apply it while outside the house - for reasons stated below. As far as a sonic signature - I don't hear any difference that could not be attributed to an overactive imagination.

However, the effect I would worry about is your health. I am not aware of the EXACT formulation - but I know that LAST is basically a "Flourinated Hydrocarbon" such as PFOS or PFOA which they originally sourced from 3M. (3M shut down production in 2002 over health liability concerns). It's contact basically turns the top few molecules of the LP surface into Teflon, which to oversimplify - is created by exposing Nylon (which includes viNYL) to a Fluorinated Hydrocarbon gas. Your new Teflon record is much slipperier and heat resistant then before, so it doesn't wear out. However:

Here's a quote from this website: http://www.ewg.org/reports/pfcworld/es.php

"The U.S. EPA peremptorily forced one member of this family off the market in 2000: PFOS, the active ingredient used for decades in the original formulation of 3M’s popular Scotchgard stain and water repellent. Shortly thereafter, 3M also stopped manufacture of a related perfluorochemical, called PFOA, that is now under intense regulatory pressure at EPA. 3M formerly sold PFOA to DuPont, which has used PFOA for half a century in the manufacture of Teflon. (DuPont now makes the chemical itself at a new facility in North Carolina.)"

Here's a quote from the EPA:

"PFOS accumulates to a high degree in humans and animals. It has an estimated half-life of 4 years in humans. It thus appears to combine persistence, bioaccumulation, and toxicity properties to an extraordinary degree."
- May 16, 2000. Phaseout of PFOS. Charles Auer, USEPA, Director, Chemical Control Division Office of Pollution Prevention and Toxics (OPPT)

Hope I'm not depressing anyone - my knowledge of this is incomplete, so it might be nice if someone from the Last Factory could clarify the risks. But I'm worried that a full disclosure wouldn't quite be in their interests.