Questions and answers:
The ink when stamped does not look very black/looks grey/looks off colour. Why?
The ink has not yet been properly mixed and requires further mixing. The ink is designed to have a ratio of pigment to solvent/resin solution of 33%/67%. If the ink is not mixed sufficiently, you have a higher amount of solvent/resin solution. This results in diluted colour.
The archival pigment does not dissolve in the solvent, it is suspended. Most inks use a colour that dissolves in the solvent, so the ink, even if not mixed correctly, will still have proper colour. If there is too little colour in our archival ink as applied, it will not look black enough. If you catch this when you are just starting to use a bottle, then further mixing will produce good results.
Current label says shake or stir. If stirring, use a wooden or glass stirring rod. Stirring has the advantage that you
can tell if there is still colour on the bottom of the bottle.
The ink was fine for awhile, now it is thick/sticky/gummy. Why?
Two possibilities:
First, see first question. Insufficient mixing will mean by the time you get to the bottom you have a large amount of pigment and not enough solvent/resin solution. You will require a new bottle.
Second, if the ink has been black enough all the time, you have been mixing it properly. But, if it is left open too long (no definite time, depends on temperature and other factors), you have lost solvent to evaporation. Too much solvent loss will throw off the ratio of solvent to resin/pigment which is designed to be 52%/48%. You need a new bottle. Keep it better capped to avoid a repeat of the problem.
Final note: If you have used most of the bottle, put it aside for awhile and then want to use it again, there could be enough air space in the bottle to cause solvent loss from the ink.