It doesn't harm bluing in itself. Some chemicals can.
Here's some info on ultrasonic cleaning form an old post:
The good points:
They really clean.
They usually clean FAST. Drop a dirty part in, and the dirt actually BOILS off in a cloud.
They DEEP clean, getting crud you normally don't even see. Ultrasonics get into cracks and holes that normally you can't get to with other methods.
They're especially good on harder fouling. (Ultrasonics work better on hard dirt).
You don't have to disassembly things. Ultrasonics are used by watchmakers to avoid having to disassembly some small components.
They work with a variety of solutions. Water with detergent works on many types of dirt, so you don't HAVE to use a volatile solvent.
The solution is heated up by the ultrasonic action. Warm solution cleans even better. Many tanks have a built-in heater also.
You can put an inch of water in the bottom and use small glass or plastic cups to hold solvent and small parts.
The ultrasonic waves are transmitted by the water in the bottom through the beakers or jars.
You can use the tank for MANY cleaning jobs, Paint brushes, dirty watch bands, electric razor heads, you're wife's jewelery, car parts, ANYTHING that you can fit into the tanks will clean up surgically clean.
The bad:
KEEP YOUR FINGERS OUT OF THE TANK. Ultrasonics and bones don't mix.
This isn't something that happens instantly, it's over time.
Expense. The larger tanks are COSTLY. However, if you want to clean a stripped pistol or small parts, one of the smaller $150.00 range tanks will work fine.
You CAN put a portion of a frame or slide in the tank at a time.
After cleaning it, turn it over and clean the other half.
Any solvent that will attack plastic or gun finishes, will attack it FASTER in ultrasonics.
You've got to be careful to apply a THOROUGH coat of anti-rust lube after cleaning. Ultrasonics remove ALL grease and lube, leaving the part absolutely bare, including in tiny holes and crevices that ordinarily cleaning never touches.
They don't work as well on soft gummy grease as harder dirt. You can speed things up by pulling parts out and scrubbing with a brush.
They're electronic and heat the solvent. You have to be careful with flammables.
Advice:
If possible buy a basket that holds parts off the bottom or make up wire hangers. Ultrasonics work better when the parts are suspended in the solution instead of laying on the bottom of the tank.
A tank cover is nice to hold down fumes.
NEVER run the unit when the tank is dry even for a few seconds, it'll burn out.
Be careful what cleaning solution you use. You can pull the item out and find finish or plastic parts GONE.
Be careful with Tritium sights, and sights with any kind of inserts or dots. Many can be damaged or removed in the tank.
The small tanks sold in discount stores for cleaning false teeth and jewelery really don't work too well, and most of them aren't even real ultrasonic units.
