The debate about re-blacking hard rubber pens has died away of late, largely because no effective method has been publicly available. However, a new re-blacking material has appeared on the market and you can find out about it here:
http://www.lbepen.com/deoxidizer-instructions
I have seen the results of using this method of re-blacking and I confess that I am impressed. A very thin layer of oxidised rubber is removed from the surface of the pen, exposing the black material underneath. Imprints and chasing appear to be unaffected.
I continue to have reservations. In the short term, the pens appear undamaged and it is even suggested that the process well make them less likely to oxidise in future. What of the longer term, though? Will bad effects appear somewhere down the road?
My advice to those who wish to use it would be to avoid employing it on rare or expensive pens for the time being. It would be prudent and fair for restorers to make buyers aware that pens have been re-blacked using this method.
Goodwriterspens's Blog 
I agree, it sounds impressive – all I need now is someone here in the U.K. who is about to place an order so that I can pay them US $20. for a pot for myself……………. this will save me paying shipping of c. US $12 – $15 plus the dreaded C. & E. charges that I always seem to be lumbered with when I buy from the States.:-)
I’ve used Micro Mesh products – both w. & d. papers plus finishing with polishing creams, and was impressed with the results of that too – although that route can take a long time to complete, and when used on chased finishes there is obviously some loss of pattern and/or imprint.
The obvious question regarding the use of Mark Hoover’s product concerns the effect or otherwise on chased patterns on the old e.d. pens, in particular. If as stated this treatment does in fact remove a layer of the BHR, then I can’t see how the chasing will remain unaffected.
Let’s see if we have one of Deb’s. contributors who can give the product a trial and report back:)
It seems that the layer removed is very thin. I have seen the results on an inscribed barrel. The inscription remained unaffected as did the chasing. Unfortunately the chasing was already well worn, but so far as I can see it could be used on chased pens with good results. That said. I won’t be using it. I don’t reblack.
I have one of his pens, a Bayard safety from c.1920. It was shiny and black on arrival: a year along, it is still black but not glossy: it looks more realistic now. I don’t like when restorers shine up a vintage pen so you can see yourself in it, the pen wasn’t that glossy to begin with!