Can rebatching firm / harden soap?

[Garden Gives Me Joy]

Can rebatching with the following ingredients (alone or in combination) harden soft soap, with little or no additional liquid or oil?

Although already 1 year old, some of my old soap is still soft to the extent that a little force can be used to eventually mash it up at room temperature with a fork. It is also sufficiently tacky that, if compressed tightly enough into a hard mold, it can form a log again. The backstory is that most of these soaps got up to 9% superfat that, among other fats, included castor oil.

... and if these ingredients cannot harden the soap, can they at least be added without causing problems?

Happy for methodology suggestions for ingredients with which you are familiar.

• Kaolin clay. Would the clay make preservatives necessary?
• Oats, ie colloidal oats. Would oats make preservatives necessary?
• Starch, Corn. Would it make preservatives necessary?
• Sulfur powder, ie yellow brimstone type. I heard that sulfur can make soap more acidic which I assume softens the soap if well incorporated in the liquid. However, I wonder whether adding it dry can have the opposite effect.
• Sea salt crystals, ie pulverized. ... or must I dissolve and essentially kill lather to a greater extent than otherwise?
• Table salt, ie pulverized (s/a)
• Sodium lactate. Appears soluble only in water at >1.5g/ml which I assume means I must add at least 1.5 g sodium lactate per ml of water. Am I correct in assuming that the sodium lactate can work without being part of the saponification process? I tried using it previously with a soft sulfur soap that had way too much humectant. Unsure whether it is because there were too many softening elements but highly conditioning and therapeutically effective soap never hardened.
• Menthol crystals, ie pulverized at apx 1-2% and possibly beaten into the soap after the soap is warmed over a hot water bath. I successfully dissolve the crystals in oil but, if possible, would rather not add more oil than these tacky soaps already have.

Thanks

 

[atiz]

Tbh I have never done rebatching so not sure. But I don't think that clay or oats would require preservatives. I also don't think menthol would help much with hardness; I have used it but have not noticed a difference and would rather keep it for some better application. Salt may indeed help -- you can at least get a salt bar! But really don't know how it works with the rebatching process.

 

[shunt2011]

I don’t think anything will harden old soap. You can add some additives but don’t think it would make it a better soap. If it hasn’t hardened after a year something went wrong.

 

[cmzaha]

I really do not think a soap that old that did not harden is not worth trying to save. Either use it as is or toss it. I agree with shunt that something went wrong a long time ago.