How I Polish Lapis Lazuli

First of all let me say that this is a stone that I have had a hard time getting a shine on. Every attempt left me with a dull finish no matter what I tried, even after using a set of diamond flat laps I still couldn’t get a result.

Then I read about resin impregnated belts for use with diamond lapping paste, these belts are knows as REZ belts and are available here in the UK from Manchester Minerals, they come in sizes to fit 6 and 8 inch expanding drums, you can also get the lapping paste from them as well.

I will provide links at the end of this post regarding sources of supply.

Now regarding the Lapis Lazuli, well the first step is the shaping on the harsher silicone carbide belts then I continue through the steps on these belts through to 600 grit. Up until recently this was as far as I could go and the results were very disappointing indeed!

But recently I bought a couple of REZ belts for my expanding wheel and two grades of lapping paste, 30 micron and 50,000 micron.

The first step with these belts is to charge them up with the diamond paste, something I have never done before but it is pretty simply. My method was to apply lines of paste to the belt at intervals then use a finger to spread it over the belt, you can use a small amount of lapping compound to dilute the paste thus making it easier to spread. This was how I charged both of my belts.

Next I fitted the 30 micron REZ belt onto the wheel and then got started, as I said it’s the first time I had used the REZ belts and had read about the dangers of heat buildup because no coolant is used. I adopted a sort of touch and remove motion with the stone, keeping it in contact with the belt for very short periods and this prevented the heat buildup.

Even though 30 micron is broadly similar to 600 grit silicon carbide in terms diamond / grit conversion tables, the diamond after a very short time started to get a shine on the Lapis Lazuli.

The next step was to change the REZ belts over and fit the 50,000 micron belt, again using the tough and remove method and very soon we started to get a reasonably deep luster on the stone.

Currently that’s where I am at however, I have ordered two more REZ belts which will be charged with 7 micron and 2.5 micron. I did this because the gap between 30 micron and 50,000 micron is huge and by adding the two extra stages a better shine should be achieved.

Once I have these other belts in the process I will write a follow up.

I am sure that what I have described is nothing new but I wanted to share this because I find it hard to find information on the internet.

I guiess my next step is to build another cabbing machine with 4 expanding wheels purely for the diamond steps mentioned above – one day maybe!

Resources:

RES Belts, Diamond paste and Lapping fluid can all be found on the following page at the Manchester Minerals web site:

http://www.manchesterminerals.co.uk/acatalog/Lapidary_accessories.html

Best regards

Dave