The primary cause is from the heating and cooling and the associated expansion/contraction as well as the change in moisture.

I have always wondered if an oven bake could "reflow" the surface, but never had a machine that i would be willing to try on...hehe

That's a shame. I don't think reheating the japan will help.
Tammi you might be able to tint some shellac black and fill the cracks a bit before you clear coat it but it will most likely still show.
Rodney

What sort of temperature where these machines baked at originally? No, I'm not going to do it on the RAF (I don't want to take it apart again now that it's sewing and clean if nothing else!) but I'm curious.

Because I'd likely not get exactly the same shade as the 75yr old base and shellac plus sun-discolorization etc, it's probably best to leave well enough alone. I appreciate the use of everyone's brain power though! ;)

For me today, it's a major thing to have taken it from the state it was in to clean and working and this weekend, I'm going to work on a base for it and hopefully the needle and throat plates will show up Monday. Then I'm going to give my hands (and fingernails) a rest!

Not sure about that, sorry

Where they baked or heat treated? I didn't think they were. The cast iron bodies where dipped in the black paint, left to dribble off, probably left to dry, then spray painted with shellac. I assume a type of "lemon" shellac, at least a purified version were used. Does anyone know if the decals were coated with shellac when factory new? My 1950 201K has a very clean metal gold look to the decals. Some machine are more dull, even though decals look like they are in good condition. Repairing cracked shellac is usually done with alcohol and repeated layers of of new shellac, usually no heat is invovled. Luck is that clean old shellac takes well to new layers of shellac.

I keep getting hits for nail polish when I search, I never new it was used in nail polishes.

I've touched up machines with black nail polish. It's usually not exact and not something I would do to a machine I care a lot about, but it's ok.

Would it make sense to spray it with a clear coat to prevent further decline? That would also make the bed smoother.

Shellac nail treatments seem to be a high end treatment - ie something I've never tried. ;) My finger nail beds usually turn blue with clear nail polish so I don't paint them. I feel like it might be unhealthy for me.

I'm not sure if the Singer machines were baked now that you mention it. I had it in my head that they did but can't recall it from the video that admittedly I haven't watched in a couple of years. I'm reasonably sure decals were covered with shellac - otherwise they'd be rubbed off right away - either in use or when we clean them with Glenn's process. The decals were only slightly compromised once I'd gotten aggressive with the first machine - through the shellac - or most of it.

I think the more dull looking ones are from certain types of care or storage - harming the shellac.

Anastasia! I have a bottle of black nail polish and a bottle of testers paint here for exactly the same reason. I agree, it's good for rust protection if it's not a critical machine as far as appearance.

I don't think I'd tempt fate on the RAF. I'm no expert, but I would be afraid the testers paint and/or the black nail polish would really screw it up! Just my opinion, but that's a pretty special machine. The only thing you really could do would be clear coat shellac and I'm not well versed enough to recommend that! Afraid I'm not much help.

Jeanette

From furniture restoration I know they are not afraid to add fillers or coloring in damaged parts before adding new layers of shellac; and that's when they don't sand down or strip the wood brefore they polish it up. I'm just keeping up a hope that dings, chips and cracks can be improved upon.