I've also been told to differentiate hippo ivory from elephant ivory by their heavier weight, non-criss crossed grains and the 'stitch-line' down the length of the ivory. However, I've not come across pictures from reputable books which show those exactly. I guess maybe I haven't looked hard enough.
But my question is - is the "stitch-line" unique to hippo ivory? I've seen quite a number of gigantic sized pekaka hilts (the jawa demam form from N. Malaysia; not the tajong, which shd NOT be called a pekaka at all.) and wondered if the hippo tusk could grow to such epic proportions (the length can be wider than my palm). Considering the wastage and the distance between the tanjak (the sharp 'nose'), the garuda mungkur (the spike rising from the back) and the buah pinang (the base of the hilt), it must have been a HUGE tusk to begin with. It has never ceased to amaze me...
On a side-topic, Lew's picture showing the various daggers has convinced me permanently that despite not specializing in collecting in any specific dagger types, he has impeccable tastes and eagle eyes to pick out the really good specimens...
Congratulations.