Sealing Jnats

Cashew Ozuku 1

 Why seal the sides of a Jnat? 

They’re rocks - can’t they get wet? 

Yes, rocks can get wet. But – when water creeps in the sides of a stone, over and over and over again – the stone’s structural integrity can be compromised.

This does not mean every stone must be sealed.  I never insist that stones MUST be sealed. 

I just say this; sealing a stone makes sense to me.

Water can be very destructive – it can dissolve nearly anything over time.

Japanese Natural Whetstones are sedimentary stones; they were formed in layers. At the edges of some stones, you can see the layers, and this is one place where we don’t want water seeping in. Other times the stone appears to be one single layer, and I’ve seen those stones crack on the sides also, although in either case, it’s hard to say, with absolute authority, that water was the culprit.

Many people have told me to seal each stone. 

Those people have been handling Jnats for many decades, so I trust them.  So – I seal them.


Cashew Lacquer

This finishing lacquer is ‘similar’ to Urushi, which is the traditional sealant. It looks like Urushi when cured, and it feels like it too. Maybe not ‘perfectly so’ – but, in my opinion, it’s very close.

Cashew is a semi-synthetic finish that comes in small cans as shown in the photo above. This is a very durable finish, which can be reinforced with a type of rice paper for additional support.  This product isn’t all that easy to find, and while it’s not expensive, it’s not all that inexpensive either. Cashew cures slowly, and it has a rather pungent fragrance.

After working with Cashew lacquer for a while – I’ve learned a few things that should be considered before and when using it.  First – out of the can, it’s very thick. Not as thick as Hon Urushi, but it’s still pretty thick stuff. 

Thinning Cashew lacquer is highly advisable; thick coats do not look as refined as thinner coats do, and they take a very long time to cure. There is a Japanese thinner that’s made specifically for this purpose but it is not readily available.  

A good friend (Nelson) suggested I try a highly refined turpentine – the type that is sold in artist supply shops. Getting the mix right takes a little bit of practice.

Out of the can – Cashew Lacquer is thicker than pancake syrup, and it goes on like cake icing. 

Thinner coats are called for but when the mix is too thin it takes a lot of coats to get the stone sealed. Because the Cashew and the turps are somewhat odiferous, and not in a great way, extended sessions of coating and curing are not much fun to deal with. At this moment – I think 75% Cashew and 25% turps seems to be about right. Two coats seem to do the trick on most stones – perhaps 3 layers if the stone is very porous. 

The curing stage can be lengthy; but tolerable. For my last Cashew session – the relative humidity in the house was very low, and the temperature was about 70º F. With those conditions, each coat cured completely in 36 hours. If the mix is thicker – it will take exponentially longer for each coat to harden. Coats of 100% Cashew took nearly 5 full days to cure completely.   

Using Cashew lacquer to seal Jnats is a major improvement over using nail polish.  It has proven itself to be a more durable and protective sealant. However - It’s not easy to procure, and it is a little difficult and messy to work with. 


Nail Polish

This is the down and dirty easy peasy  method of sealing a stone or Nagura. It’s cost effective and simple; nail  polish dries fast and seems to work well. While not as elegant of a solution, I’ve not had a single problem with any of the stones I’ve sealed this way. Even though it’s not as glamorous as Cashew Lacquer or Hon Urushi, it’s a lot easier to deal with for sure.  One small bottle can be used for 3 coats on 2-3 Jnats, depending on the size of the stones, thickness of the coats, etc.  


In Japan – a paint called Biniroze is anothe option used for sealing the sides of whetstones and Nagura. y, it’s reported to be stronger than other options.  It’s not available here in the USA, but I think there’s a paint of a similar composition here that might be a good substitute. 

© Keith V Johnson 2014 - 2018