It's all codersprites?

Always has been.

code/modules/smithing/furnace.dm

@@ -2,7 +2,7 @@
 	name = "furnace"
 	desc = "A furnace."
 	icon = 'icons/obj/smith.dmi'
-	icon_state = "anvil"
+	icon_state = "furnace0"
 	density = TRUE
 	anchored = TRUE
 	var/debug = FALSE //debugging only
@@ -25,8 +25,11 @@
 		return TRUE
 	if(reagents.remove_reagent(/datum/reagent/fuel, fueluse))
 		working = TRUE
+		if(icon_state == "furnace0")
+			icon_state = "furnace1"
 	else
 		working = FALSE
+		icon_state = "furnace0"
 
 /obj/structure/furnace/attackby(obj/item/I, mob/user)
 	if(istype(I, /obj/item/ingot))
@@ -44,9 +47,23 @@
 	default_unfasten_wrench(user, I, 5)
 	return TRUE
 
+/obj/structure/furnace/attackby(obj/item/W, mob/user, params)
+	if(W.reagents)
+		W.reagents.trans_to(src, 250)
+	else
+		return ..()
+
+/obj/structure/furnace/plunger_act(obj/item/plunger/P, mob/living/user, reinforced)
+	to_chat(user, "<span class='notice'>You start furiously plunging [name].")
+	if(do_after(user, 30, target = src))
+		to_chat(user, "<span class='notice'>You finish plunging the [name].")
+		reagents.reaction(get_turf(src), TOUCH) //splash on the floor
+		reagents.clear_reagents()
+
 /obj/structure/furnace/infinite
 	name = "fuelless furnace"
 	debug = TRUE
+	icon_state = "ratfurnace"
 
 
 /obj/structure/furnace/infinite/ratvar
@@ -55,4 +72,4 @@
 
 /obj/structure/furnace/infinite/narsie
 	name = "rune furnace"
-	desc = "A runed furnace. Powered by... something, but seems otherwise safe."//todo:sprites
+	desc = "A runed furnace. Powered by... something, but seems otherwise safe."