I have a Singer 15-91 that I am eager to get all cleaned up, but I decided to test it on my Singer 99-13 first. The decals on the 99-13 were not in the greatest shape to start with--most were already silvered, or missing completely.
The best looking decals on this machine (that are still mostly intact, and still all golden) reside on the back of the pillar, and are hidden behind the motor. I decided, therefore, to start my testing there. Below are the before and after pictures.
Before the decals were dark, dusty, dingy, and covered in a slightly sticky residue.
After applying the TR-3 with a cotton ball, and rubbing in small, circular motions, the decals looked brighter, and still golden. They appear a bit lighter in this photo than they actually are. I don't know how dark the gold would have appeared new, but the results looked pretty good to me. And the pillar shined up really well. So I moved on to the back of the machine bed . . .
Here's a before shot of the back, left corner of the machine bed (and mostly silvered decals). I never did clean this machine when I first brought it home.You can probably see the waxy film that was there. I had no idea if this was just the top of the finish wearing away, or old polish, or what. Having no idea what it was, or how to clean it, I just used the machine as is.
And here is the after photo. I rubbed these decals a lot, using at least three applications of TR-3 on cotton balls. The good news is, the still golden parts of the decals didn't get any lighter. The bad news, however, is that the parts of the decals that were already silver rubbed away with the grime. The black paint polished up to a mirror like shine.
The film near the faceplate was a little different. I could easily scrape it away with my fingernail. Again, I don't know what this stuff was. This machine spent time in the junkyard, and then in a smoker's home. When I brought it home, the cabinet and machine were both saturated with smoking odors--so much so, that I got a headache every time I used the machine. I suspect, then, that the gunk covering the machine might be tar from the cigarette smoke. Who knows?
Since I wanted to be more careful this time with the decals, I used a plastic kitchen scraper to scrape off what I could of the tar, and then cleaned and shined it up with the TR-3.
In some places the residue was a little more stubborn and took a lot more passes to remove. When the TR-3 dried on it, it became the brownish discoloration you see in the photo on the left. However, with enough cotton balls, the TR-3 did remove it, with no ill effects on the black paint.
So here's the moral of this tail. I will repeat what I read on that other website. Test, test, test!
Be very careful on the decals. One or two passes doesn't seem to do any harm. I suspect on a machine not this dirty, or with less stubborn grime, the decals would be just fine. Even so, in the future I will use this stuff on the decals last, after I've polished up the rest of the machine.
Also, assess the mess on your particular machine. You may not be able to get the decals completely clean using the TR-3, at least not without rubbing them completely off, so you'll want to make sure any dirt and grime doesn't discolor too badly. Find an inconspicuous spot on the machine to apply the TR-3, and see what any remaining grime looks like after the polish has had time to dry.
If the grime changes colors, (as shown in the photo above) you may want to consider cleaning most of it off using another method before polishing the machine with TR-3. The TR-3 will remove some very tough grime (even if the previous application has dried overnight), but, once applied, it also makes it more difficult to clean the grime off by other means. The discolorations you see above were completely removed with more applications of TR-3. However, I couldn't do as many passes over the decals, so a bit of brown remains around the lettering.
Here's what my Singer 99-13 looks like now . . .
I hardly went over the decals on the front of the machine bed at all, so they look about the same as when I started--silvered and worn away. You can probably see that I've got a bit more cleaning to do on the front, but it will all clean up and polish up nicely tomorrow. I needed a break. :~)