This is totally new to me...

[Ray]

Tony's success using Grodan Mini-Cubes and perlite as his phrag medium spurred some experimentation.

My locally available perlite is simply too fine to use alone, so I started experimenting with a 3-phase approach, using LECA, Grodan, and perlite for a couple of phalaenopsis. The fine perlite tends to stick to the rock wool, providing more space between adjacent cubes. You can see that in the upper right of the attached image.

A few weeks ago, after repotting the plants into it, I was in a rush and neglected to get the perlite (coarse) dust off the leaves. Today I noticed permanent eruption bumps on the leaves where the material was. It's almost as if the cells grew up around-, and trapped them.

 

[Tony]

That's wild, I've never seen that happen.

 

[tnyr5]

I have. It's just a response to irritation. Happens when I accidentally get bark/sand/perlite dust in the crown of my Paphs, too.

 

[Ray]

In this case, it was on the flat of the leaf, not the crown, but it was a relatively new leaf, so maybe the cells were still more active than in older tissues.

 

[skirincich]

Reminds me of fibrosis of the lungs when particulates become permanently lodged on the tissue.

 

[PeteM]

Thanks for posting, I’ll note to keep the emerging leaf clean after repotting

 

[David B]

Something to think about. One of our local nurseries here in the Toronto area is an expert grower of cacti and succulents, and also orchids. He has developed several grow mix formulas. He is an advocate of volcanic pumice. I have been incorporating pumice for over a year now and it retains it's integrity very well. I find that it does not accumulate any unwanted mineral effervescence on its surface and is highly durable as a substrate. It is more expensive than perlite but when you take into account the values of your plants, it's ability to contribute to a healthy root zone allowing air circulation and drainage is very important. For cattleya my mix is 40% orchiata and the rest equal parts charcoal, leca and pumice.