making sulphate ion visible

[m777182]

Does anybody know if there exist a compound that would, when applied over a surface, proved the presence of sulphate ion as colored spots?
m777182

 

[unclesyd]

What is the surface?
A little more details please.

 

[m777182]

Inert smooth ceramics covered with droplets of NaSO4 that were evaporated and left tinny crystals of said Na2SO4.
M777182

 

[unclesyd]

Here are specific ion test strips for sulphate. They are available through most large chemical supply houses.
I don't have any of my quantitative chemistry books around and I don't know if there is any spot test for sulphate. The old quick and dirty method was to add a little barium chloride to a solution and look for a white precipitate.

https://www1.fishersci.com/Coupon?gid=209248&cid=1328

http://www.vgdllc.com/ion_test_strips.htm