This Boker Diamond arrived today and it will not open enough to use. The first picture shows how far it will open before it becomes tight. I don’t want to force it and I don’t know what lubrication to use that will not hurt the scales. There is some corrosion on the blade near the pin. Any suggestions?
I think someone with good intentions tightened up the pin a bit too much. I agree with Alfredo. You may have to repin it but try working it with a bit of oil every day. It may loosen up a little. Any gun or reel oil will be fine. I like motor oil for razors, myself. There is always plenty left in the jugs after doing an oil change. Avoid any sort of vegetable oil. Mineral oil will work, yeah, and lots of guys favor it, but I prefer motor oil because it is formulated to leave a clingy film to steel, and gun/reel lubes are designed for small, fine moving parts in which sticking or failure is a serious thing.
I like mineral oil as well for this. Add drops between scale and steel both sides then work slowly back and forth. Do this over a paper towel or something) as it starts to free it will drip rusty oil and sound a little rough.
Continue moving and adding oil till you do not hear an abrasive sound. Wipe clean, add a few more drops to clear, a couple more movements and wipe again
Should be good to go.