This is a question that gets raised quite frequently.
Many Titanium-ring suppliers give a warning about taking care with getting the size right as it can't be altered in the future - this isn't strictly the case as it all depends on different factors.
- Grade of Titanium
- Wall thickness (Under 2mm thick also restricts the options to stretch and compress)
- Is it Diamond set?
- Does it have a precious metal inlay?
- Does it need to go up or down in size?
Whilst it isn't normally within the capabilities of a traditional jeweller to do a quick resize, there are often various options that the manufacturer can take.
Grade 2 commercially pure Titanium is fairly ductile and will stretch and compress quite readily. If it has a precious metal inlay set into the outside, it is probably better to take a skim out of the bore to make it bigger. Stretching will normally cause the inlay to split. The amount of increase could be up to about two sizes.
Compressing a ring with an inlay is usually ok for about one size. Compressing plain rings depends on the outside pattern. If it is patterned, then the amount of force required to compress it will undoubtedly cause too much damage to repair the outer surface economically and so should be avoided.
Plain domed or flat rings don't present much of a problem. Diamond set rings are quite limited in their potential to be resized. Stretching or compressing causes deformation at the weakest points where the holes have been drilled for the diamonds and so, here again, the only option is to remachine the bore to make it larger. (1 to 1.5 sizes)
Higher tensile grades of titanium, such as aircraft grade Ti/6Al/4V (or grade 5 as it is also known) will not stretch or compress. The only option with these is to increase the ring size slightly by remachining the bore larger. In many cases, especially with plain rings, due to the amount of refinishing required with resizing it is simpler to make a new ring. This isn't always an option, for example, when a ring has been bought as a wedding ring and has been personalised with engraving and blessed in church.