hi all. i've found 2 techniques which work pretty well for slip trailing, using bulb applicators. You will still need to adjust the water content/fluidity of your underglaze or stain to work properly with the orifice size..a runny watery stain solution will run out of any size tip, while a too viscous underglaze won't fee properly and will alternately blop, spit and splat.
i use bulb applicatora primarily to fill recessed areas. i i am doing lettering i still like to recess the lettering and fill it.
for medium -large scale i use a large rubber bulb applicator and modify it by cutting off most of the tip and inserting a glass eye dropper end 9remove the typical black squeeze rubber from the eyedropper. the glass should fit very snugly into the rubber of the bulb.you can put electric tape around the joint if you want. the eyedropper end gives a pretty precise tip and allows tou to use the bulb applicator with good efficiency for somewhat thick lines or if you need to fill large areas.
for detail work i have tried a number of different products but finally invested in a Xiem bulb applicator system, and i am glad i did. i have a commission i am currently working on and i used squeeze bottle with various tips, which worked K, but the Xiem, which is a bulb applicator with different size tips, works so much better. it allow much finer control of squeeze pressure. it also is much more ergonomic. you might not notice this unless you have to do hundreds and hundreds of pieces. with the bottles, my thumb/forefinger muscles stareted to cramp eventually, with the bulb , they can relax much more.
this is a nice,precise way to apply. i am using Laguna underglaze thinned a bit with water.