A History of Ultrasonic Record Cleaning

Given all of the attention to ultrasonic cleaning of LPs, made more accessible by DIY, there’s been surprisingly little written about the history of ultrasonic record cleaning. Mike Bodell changes that with a piece I just published entitled “The Curious Case Of Record Cleaning In The Quest For Sonic Perfection," which you can find here:
Mike found an old patent that directly addresses the subject, and puts the development of various cleaning approaches into historical context. I think you’ll find it a worthwhile addition to the literature and an enjoyable read.
For me the elephant in the room is the potential for damage to the LP. The article is reassuring but lacks any supporting data except to say that users of US cleaners have not reported hearing a problem That alone does not convince me. Testimonials are not data. Someone needs to do a study with controls using microscopy as a tool. Also, I thought 80 kHz was preferred by some manufacturers yet that frequency isn’t mentioned. And finally, pure water or what should be the medium? I think using a mild non ionic detergent cannot hurt. Good article for an historical perspective. Thx.
@lewm --I don't think there have been any serious scientific studies of damage. I don't think the article was intended to convince otherwise and agree that anecdotal reports are not a complete answer. Mike did mention to Degritter (@120kHz) but not others. 
Could you elaborate on what you mean by "And finally, pure water or what should be the medium?"
My understanding is that ultrasonic cleaning is enhanced by a surfactant. 

My own experience is that I can detect no aural damage, but I only use ultrasonic for limited amount of time (e.g. 5 minute cycle) as part of a larger cleaning regime that includes pre-cleaning and post cleaning rinse using reagent water and vacuum (Monks). 
Fair question though and not one that I think the author intended to resolve. 
No argument here. I didn’t mean to imply criticism of the article per se. Interesting to know you use a surfactant. So far as I know there is a school of thought favoring pure water. I would be on your side if I ever adopt US.

i think a post cleaning rinse in pure water is very important.
@lewm - right now i am not using any surfactant in the US machine since I still am using the KL. But I've had a number of discussions with a manufacturer of ultrasonic equipment for factory lines who, at least in a metal parts (non-LP) context, convinced me of the value of using a surfactant. The biggest issue, of course, is removing it from the record surface. Thus, the pure water rinse. 
My plan when the KL goes is probably to buy the big Elma, given the feature set, plus external filtering and recycling. 

Which Elma product would you buy for cleaning LPs? I looked at their website. It seems they make a very wide variety of ultrasonic cleaning machines, but most of them are for various industrial purposes. Thanks.
@lewm- Tim, in this article I published, switched from a cheap Chinese unit that crapped out after a year to the P120, see [url]https://thevinylpress.com/timas-diy-rcm-follow-up-2-compelling-changes-improved-results/[/url].
@Terry9-if memory serves is using a Fisher Scientific branded Elma version of the P60, which as Terry could probably explain, is a tight fit for two records, but I gather works well, and is less pricey due to its smaller size/capacity.
Whart, maybe you could try to actually damage a few records with the ultrasonic. What would it take or is it possible at all ?
Too low a frequency for too long; if the record doesn't rotate, the cavitation effect focused in one spot could cause damage. I think the literature on ultrasonic cleaning for industrial purposes (non-LP) could be a starting place to look at the risks, which might also include water temperature. I haven't really thought too much about how to damage but it's the flip side of not damaging; lewm raises a fair point about potential damage; we've all engaged in a leap of faith based on manufacturer statements and user anecdotal experience. That's not going to satisfy someone who wants "proof." If I had time, I could ask or explore more; there is a point where experience in cleaning metal parts doesn't translate, but I suppose if it damages metal it is bound to damage vinyl. 
Although,I wasn't trying, but left 2 different but brand new lps in my 40hz cleaner @ 45C for 45 minutes with my spinner off. When I realized it after those complete cycles, I put them through the exact same cycle with the spinner on, then listened. I heard nothing that concerned me.
I see. I think, I wouldn't clean more than once valuable to me records, just in case. It appears that there is no guarantee that there can be no damage even if used correctly.
Interesting read here. I believe a lot has been "discovered" or at least refined on ultrasonic cleaners science in last few years which will help settle your mind on ultrasonics, to a point. I use both a Kirmuss and an Audio Desk. Kirmuss posts a LOT of useful information online and is a must read before you purchase an ultrasonic whether his or others. I am happy with both but believe the Kirmuss does a better job without a doubt, though it typically takes a lot more time and elbow grease - tho worth it to me especially on favorite records. Audio Desk is my go to for mass cleanings or first clean just to hear if a record is an outstanding pressing worth putting the extra time in with the Kirmuss to bring it to the best possible level of sonics. I believe both use ~ 35Hz to avoid damaging records, the science as I know it being is the higher the Hz, the faster and more powerful the microscopic "explosions" of the ultrasonic bubbles on the surface of the records are, thus, in theory if powerful enough could cause damage, and 35Hz is "safe." I’ve run records multiple cycles of up to 30 minutes on both with no problems at all - and I have a VERY revealing system so would likely hear issues if there were any. It’s apparently all in the cycle rate (35hz)and the surfacant that ATTRACTS water to the surface and most importantly INTO the grooves of the record were the hard to get out and sound altering dirt etc lies. Water alone will not do as good a job at removing the dirt, dust, release residue etc, that is in the grooves.