Hey there. A crafted item using the Lost Memento will have access to a shader which will appear on the 3rd tab (thereabouts) on their shader options, it is called 'Twilight Keepsake'. In fact, all craftable weapons have this shader in their shader options, as well as the Vanguard, Gambit and Trials Memento shaders too, so you can preview the look. However only by shaping/reshaping the weapon with the appropriate Memento and levelling the weapon to 30, will let you actually select that look on the weapon.