This issue has been discussed many times before but, there is always something new to add. I believe one of the bigger "dilemmas" is to make the decision to harden or not that particular blank, regardless if you purchased it or you cut it yourself from a board/log/tree, etc. There is a large group of woods that don't need any more hardening but some others can do with a little help.
Lets see, if the blanks is generally all spalted, the chances are you will need to harden it, if the blank look OK but you see a few spots that feel soft to touch or fingernail scratch, you can decide to put it in the lathe, turn as far as you can and then soak the soft area with CA. This sometimes works, some don't, and in most cases, the blanks are lost (blow outs) as the wood didn't have enough strength to keep together, with the gouge or other tools tearing it to bits!
So, if the blank is soft for whatever the reason and spalting is not the only cause, and you don't want to risk losing it buy not have stabilize enough to resist to the cutting/shaping process, not having all the stabilizing gear (pressure pots), shouldn't deter anyone from having it harden. I simple glass jar or a glass test tube, enough to fit the blank in and have it submersed with any of the wood hardener available at most hardware stores.
Don't put any lid on it, leave it there for a couple of days, then get it out and put it to dry somewhere where it will not get stuck to anything. Drying time really depends of where you are, at least one week, and I would keep it the the hottest part of the house or shed. You can also accelerate the drying process by using hot air guns or a gas blower, just be careful of not burning it...!
If wood hardener is not available or you can't afford it, that's right, at $69 a litre up here, you either are desperate or crazy! is that case you can harden the wood quite well, by using a 50% water and white wood glue of a medium to good quality, that dries clear, this is important!. Mix it really well and submerse the blank(s) on it, using a 2kg ice cream container, after a couple of days or so, take it out scraping the excess glue with your finger, put it to dry on top of a piece of plastic, never use newspaper or cardboard as that will soak all the glue out of the blank!
It will take a little longer to dry, but no more than 2 weeks!
Another very important step to minimize the risks of loosing a fragile blank is, cut the square corners of the blank before you put it in the lathe, in this case it should be done carefully before is harden, saving you lots of solution, mainly the proper hardener that costs a fortune!
I'm not aware that a blank that has been harden, either buy the industrial hardeners or using PVA glue, creates any "negative reaction" to any of the traditional finish products. I understand that all this can create a little extra work but like as been said already in a previous post and I've been claiming it for long time, these stabilized, for the reason they had to be stabilized (harden), are capable to produce a finished product, not possible to be matched with anything else...!
So, good luck!
Cheers
George