Who was looking for a method to soften hard phone cords. I ran across the following.
Another authority, Zeigler, has the following on this subject: Tubing, bands, and other articles of vulcanized caoutchouc that have become brittle and useless, may be restored to usefulness, indeed, to their pristine elasticity, by treating them as follows: First, put them in a hot aqueous solution of tannic acid and tartar emetic. Next, transfer them to a cold aqueous solution of tannic acid and calcium sulphate. Mix the two solutions and heat to about the boiling point, and transfer the articles to the hot solution. This treatment should bemaintained from 1 day to 3 or 4, according to the nature and condition of the articles.
D/P
Dan, I may have asked a while back as my '55 WE565 has a thick dull black handset cord that is a bit stiff, though it has no cracks, splits or any other types of damage. I have no idea what those chemicals you've posted are or where to purchase them.
This discussion came up on the TCI Listserv awhile back. There is one member (Bobby K.) that I believe worked in the chemistry department at U of Cal. Berkeley that tried to find the answer to this problem. He said that the best he could do only lasted temporarily. His conclusion was that you could NOT bring old rubber back to life. I trust his answer.
Dougpav
Several members have reported that a happy side-effect of the bake and freeze method of re-coiling cords has been a considerable softening of stiffened cords. You might try that process, even if your cord has tight coils.
Doug;
Unfortunately I lean towards agreeing with you. Once the initial chemicals have evaporated I see no way to reintroduce them.
I had a brain storm idea once. It was for yellowed dry paper. Why not simply analyze the paper and see what is no longer there, then mix up a batch, and spray it back on. That idea didn't go to far.
D/P