Xtol is an ascorbate developer. Ascorbates develop silver very efficiently, and ascorbate developers break the speed-grain window of traditional developers and provide about a third to a full stop more speed with most emulsions. The improved shadow detail comes from better speed and the improved highlight detail comes from the marked s shape in the characteristic curve.
Xtol was reformulated by Kodak after they switched contract manufacturer when Tetenal went broke. Some recent batches have had problems.
X-T3 is an ascorbate developer by Adox that behaves for all purposes identically to Xtol. Adox has better packaging than Kodak, and a proprietary process that decreases aerialisation of fine particles. Both advantages.
Long Xtol rant by me:
[Leica] Long Xtol rant
Other Xtol information from Michael Covington:
Kodak Xtol Developer - Unofficial Resource Page
Tonally, Xtol produces negatives with nice even tones, that can be printed a lot of ways. The tones are similar to those of D-76. There are some here who will tell you that the negatives it gives are ‘boring’ and maybe they are, but I like negatives with even tonality that give a lot of possibilities for printing. I particularly dislike negatives developed in ways that lower the mid tones. Xtol provides nice, bright, open tones.
The photos below are Neopan 400 in Xtol 1+3 and Acros in Xtol 1+1.
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