I misread a post on the FPN which made me think that Diamine Majestic Blue was a fair replacement for Parker Penman Sapphire. Checking through the board, however, it seems other people think so as well. Anyway, I had some Majestic Blue, so I tried it, and it needed diluting. I eventually settled on a 3 : 2 dilution of DMB with water.
Wonder of wonders, it was almost spot on. The colour is still a tiny tad off, the DMB being a little bit flatter than the PPS. However, in separate samples (not side by side) it is difficult to tell which is which. The diluted DMB looks like it needs the addition of a little bit of a bright Blue, perhaps a little Diamine Sapphire.
However, the important thing is that both inks, PPS and diluted DMB, behave on paper almost identically. The both dry quickly, there is usually (except on the worst of papers) no feathering, there is no spreading and bleeding only occurs on the worst of papers. And when bleeding does happen, it happens to the same degree with both inks. Both inks also show similar degrees of shading and red sheen.
Once I find another bright Diamine ink that behaves on paper as well as these two, I will see if I can shift the diluted DMB towards a slightly brighter blue.
Here is a scan of a writing sample --
It is a bit teal coloured from the original, but what I wanted to show was the very slight difference between the two inks. Most of the text is written with DMB diluted in a Lamy Vista Fine, but the area underlined in pencil was with a Parker 100 Fine.
The Samples at the bottom are self explanatory, except the bit that says DMB 1:1 should say DMB 3:2