Glass with fabricating debris is going to scratch when you run something like a razor blade over it because it is harder than the glass, it will sound like you’re scraping sand or paint off the glass, pretty easy to identify . Seeing scratch marks from running a silicone squeegee blade over it is unheard of. I’d be curious as to who the manufacturer is?
I will add my 2 cents in here,I have 25yrs experience as a glazier and I have known from day one that toughened glass will scratch easier than float glass,when glass is toughened it does not come out of the furnace perfectly flat or as close to like annealed/float does,this non flat surface means running a scraper blade over the un even surface will cause scratches,in saying that as glaziers we use single edge razor blades to remove stickers etc from glass after we install it,in 25yrs I have never scratched one piece of toughened in doing this,how ever if you start using the wider scraper tools your risk level goes way up due to the width of the tool and the method used
Thinner glass such as 4,5 and 6mm toughened is more probe to scratch as it will distort more than thicker glass when ran through the furnace,the 10 and 12mm used in showers comes out more flat than the thinner glass and is less likely to scratch ,we don’t experience much fabrication debris here in Australia or NZ glass quality is good,most of the issue is the uneven surface of the glass,sometimes it can be confused with FD which does exist but not in high numbers
Now that I clean windows I don’t use scraper blades at all,I know that it is much faster to use the scraper tools and the methods to do so but for me the risk of scratching is too high,I still use the small single edge razor blades even though it slows the process down considerably,I just use them sparingly and inform the customer how they would like to proceed and with which method
In my opinion razor scrapers shouldn’t be used on toughened glass at all,we have all known this is the case,you can still use them when you know what you are doing and not scratch glass but using some methods I see on you tube is asking for trouble,it’s all good to issue waivers but I know what’s happening to the glass and it doesn’t sit right with me to have a waiver signed and then go and scratch up the glass just so I can get the job done quicker and the customer knows no different
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So all the glass I have been cleaning since about 2000 did not have FD on them it was just uneven?
I really don’t know what it was but now hey say FD is a myth, but it sure scratched up bad, in many cases there was no other way around using a scraper when you have rendered walls that meet up with a window and you cant tell there is a window there 
FD definately exists,but in my opinion the fact the glass is now deformed and no longer flat is just as much a problem if not more so,I can tell the difference between the two and come across FD less often than un even 4-6mm toughened.I totally understand that the quickest and sometimes only method is to scrape away with wide scraper tools,the only problem I see is telling customers that all you can do is use blades and that they need to sign a waiver before they do it-this is definately the case sometimes but sometimes cleaners just`don’t have enough knoweldge on the glass they are cleaning and can sometimes be unfair on the customer,then you get the odd few who will knowingly scratch the glass even though there are other methods they could use…whether they are lazy or decietful is anyones guess but I just like to give the customer all the info and let them choose how to proceed.
I’m not saying that these days I would use a razor. but back then in 2000 is the first time I encountered this is was on a construction on the beach in Adelaide where they had strong winds for much of the construction of a 6 story apartment complex, the whole building was rendered and had glass balustrades that where on each balcony. and the whole 1st floor (probably 2nd floor to Americans) was a wall of glass above the below shop front. You could not see the difference where the rendered wall finished and the glass began even the balustrades were covered on both sides. Every pane got completely scratched the hell out of.
I was a rookie back then only had about a year of proper experience, had run a WC business a few years before but was never “properly” trained until I started at that job. But I was with a 25 year vet and he was completely dumb founded by the job as was I. We were on that job for 6 weeks or more . Then back there every month to clean the entry ways windows and the windows not accessible to the residents.
