A diamond ring that will not come off is a finger problem before it is a jewellery problem. Stop pulling repeatedly: friction and pressure can increase swelling and make the ring tighter. If an ordinary cutter has already failed, do not keep squeezing it against the finger or try a larger improvised tool.
These signs need urgent medical attention
Go to an emergency department if the finger is blue, purple or unusually pale, numb, cold, rapidly swelling, severely painful, injured, or if the ring is cutting into the skin. Do not delay to find a jeweller or preserve the band. A clinician can assess circulation, injury and the appropriate removal method.
Do not try a compression wrap when there is an open wound, suspected fracture or signs of impaired circulation. Stop any removal attempt if pain, colour or sensation worsens.
If there is no injury and the finger looks and feels normal
Raise the hand, then try a little soap or water-based lubricant and gentle rotation. Avoid forceful straight pulling. If the ring does not move with a brief, gentle attempt, seek help instead of repeating the same action until swelling develops.
The Harvard Health stuck-ring first aid article describes a string or dental-floss method. Crucially, it says to unwrap the string and immediately seek urgent care if the ring cannot be removed. A tight wrap must not be left on the finger. If you are unsure whether compression is appropriate, leave removal to a clinician.
Why a cutting tool may not work
A diamond setting does not identify the metal of the band. Gold, platinum, steel, titanium and tungsten-based bands can require different equipment and techniques; a tool suitable for one ring may be unsuitable for another. Do not use pliers, kitchen knives, heat or a power tool next to the skin. Tell the medical team which metal is listed on the receipt, if known, and what removal attempts have already been made.
A jeweller can advise on sizing or repair once the finger is safe. Whether a cut band can be repaired depends on its metal, setting and damage; saving the jewellery must not take priority over circulation.